| 1. |
- Bertilsson, Erik, et al.
(författare)
-
A Modular Base Station Architecture for Massive MIMO with Antenna and User Scalability per Processing Node
- 2018
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Ingår i: 2018 CONFERENCE RECORD OF 52ND ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS, AND COMPUTERS. - : IEEE. - 9781538692189 ; , s. 1649-1653
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Konferensbidrag (refereegranskat)abstract
- Massive MIMO is key technology for the upcoming fifth generation cellular networks (5G), promising high spectral efficiency, low power consumption, and the use of cheap hardware to reduce costs. Previous work has shown how to create a distributed processing architecture, where each node in a network performs the computations related to one or more antennas. The required total number of antennas, M, at the base station depends on the number of simultaneously operating terminals, K. In this work, a flexible node architecture is presented, where the number of terminals can he traded for additional antennas at the same node. This means that the same node can be used with a wide range of system configurations. The computational complexity, along with the order in which to compute incoming and outgoing symbols is explored.
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| 2. |
- Bertilsson, Erik, et al.
(författare)
-
A Scalable Architecture for Massive MIMO Base Stations Using Distributed Processing
- 2016
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Ingår i: 2016 50TH ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS AND COMPUTERS. - Washington : IEEE COMPUTER SOC. - 9781538639542 ; , s. 864-868
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Konferensbidrag (refereegranskat)abstract
- Massive MIMO-systems have received considerable attention in recent years as an enabler in future wireless communication systems. As the idea is based on having a large number of antennas at the base station it is important to have both a scalable and distributed realization of such a system to ease deployment. Most work so far have focused on the theoretical aspects although a few demonstrators have been reported. In this work, we propose a base station architecture based on connecting the processing nodes in a K-ary tree, allowing simple scalability. Furthermore, it is shown that most of the processing can be performed locally in each node. Further analysis of the node processing shows that it should be enough that each node contains one or two complex multipliers and a few complex adders/subtracters operating at some hundred MHz. It is also shown that a communication link of some Gbps is required between the nodes, and, hence, it is fully feasible to have one or a few links between the nodes to cope with the communication requirements.
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| 3. |
- Bertilsson, Erik, 1990-, et al.
(författare)
-
Computation Limited Matrix Inversion Using Neumann Series Expansion for Massive MIMO
- 2017
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Ingår i: 2017 FIFTY-FIRST ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS, AND COMPUTERS. - 9781538618233 ; , s. 466-469
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Konferensbidrag (refereegranskat)abstract
- Neumann series expansion is a method for performing matrix inversion that has received a lot of interest in the context of massive MIMO systems. However, the computational complexity of the Neumann methods is higher than for the lowest complexity exact matrix inversion algorithms, such as LDL, when the number of terms in the series is three or more. In this paper, the Neumann series expansion is analyzed from a computational perspective for cases when the complexity of performing exact matrix inversion is too high. By partially computing the third term of the Neumann series, the computational complexity can be reduced. Three different preconditioning matrices are considered. Simulation results show that when limiting the total number of operations performed, the BER performance of the tree different preconditioning matrices is the same.
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| 4. |
- Bertilsson, Erik, et al.
(författare)
-
Use of digital human modelling and consideration of anthropometric diversity in Swedish industry
- 2010
-
Ingår i: Proceedings of the 42nd annual Nordic Ergonomic Society Conference. - 9788299574723
-
Konferensbidrag (refereegranskat)abstract
- This paper study and clarify problems, needs and opportunities when working with anthropometric diversity in digital human modelling (DHM) systems. A comparison between product development and production development in Swedish automotive industry is made. Interviews with DHM users and ergonomics specialists about their way of working with anthropometric diversity confirmed that simulations are often done with only one or a few human models. The reason for this is claimed to be time consuming processes, both at the creation of the human model but mainly when correctly positioning the model in the CAD environment.
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| 5. |
- Svensson, Erik, et al.
(författare)
-
Anthropometrics and Ergonomics Assessment in the IMMA Manikin
- 2010
-
Ingår i: Proceedings of the 3rd Applied Human Factors and Ergonomics (AHFE) International Conference. - Louisville : AHFE International. - 9780979643545
-
Konferensbidrag (refereegranskat)abstract
- Digital Human Modeling (DHM) tools are useful for simulating human work and proactively evaluating ergonomic conditions. IMMA (Intelligently Moving Manikin) is a project that aims to develop software that combines digital human modeling and path planning. The work in the IMMA project is divided into a number of work packages that gradually increases the complexity of the problem. This poster paper regards both the functionality for ergonomics assessment and consideration of anthropometric diversity in the DHM tool being developed. Reviews of current DHM tools and interviews with DHM users and ergonomics specialists were done to clarify problems, needs and opportunities when working with anthropometrics and ergonomics evaluations. Interviews showed that simulations and following evaluations are almost solely based on static postures and with few human models. The main reason for this is claimed to be complex and time consuming processes when creating and evaluating simulations. Both the review of current DHM tools and the interviews confirmed that there is an evident need for more time-dependant evaluation methods and a better coverage of the intended users’ diversity. Attained knowledge from the analysis of current DHM tools and interviews are used to create work processes and two specific modules intended to be implemented in the new IMMA DHM tool. Key issues for the modules are ease of use and flexibility. The overall objective with the IMMA DHM system is to offer a tool that support faster and more correct ergonomics analyses.
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| 6. |
- Svensson, Erik, et al.
(författare)
-
Anthropometrics and Ergonomics Assessment in the IMMA Manikin
- 2011. - 1
-
Ingår i: Advances in Applied Digital Human Modeling. - Boca Raton : CRC Press. - 9780429151842 - 9781439835128 - 9781439835111 ; , s. 139-144
-
Bokkapitel (refereegranskat)abstract
- In earlier verification and validation studies for digital Human Modeling Systems (HMSs) in an F-16 cockpit application, the initial positioning and posturing of the manikins were found to be the greatest source of error in calculations of manikin reach and clearance (Oudenhuijzen et al. 2002). The goal for this project was to develop a method to reduce these errors based on "training" the HMSs. In essence, this training enables the manikins to assume realistic postures by employing 3D body scans of real people in an actual F-16 ACES II ejection seat. This was the starting point for defining manikin initial position, and posture during reach, as well as to quantify the effects of the restraint system and the protective equipment in an F-16 cockpit environment. The Safework HMS was chosen as the modeling system to be "trained." Fourteen subjects with a considerable range in body dimensions were selected for the modeling activities in this project. Their scan data were collected under two conditions while seated in the F-16 ACES II ejection seat: 1) wearing stretch shorts (and sports bras for females) to serve as baseline data; and 2) wearing a full pilot cold water immersion ensemble (small subjects only). The resulting subject data were used to produce 15 reach posture libraries for the Safework HMS. These libraries can be considered as a kind of fidelity profile that quantified, and simultaneously accounted for, the effects of the restraint system, protective equipment, and tissue deformation in this seated cockpit environment. The average difference between the small subject reach envelopes and their corresponding manikin envelopes (compared at the radial styloid on the wrist for all 15 reach directions) had an error range of +/ - 7 mm. Hence, the library is considered to be highly accurate and verified for anthropometric accommodation studies on the F-16 when using the HMS Safework and the resulting posture libraries. The positioning accuracy for accommodation tasks was also found to be accurate. Manikin eye location, during positioning in accommodation tasks, lies between +/- 6 mm in the vertical Z direction, and much smaller (+/- 2 to 7 mm) in the horizontal directions.
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| 7. |
- Svensson, Erik, et al.
(författare)
-
Review of the incorporation, utilization and future demands of ergonomic evaluation methods in Digital Human Modelling
- 2010
-
Ingår i: Proceedings of the 42nd annual Nordic Ergonomic Society Conference. - 9788299574723 ; , s. D1-6-D1-10
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Konferensbidrag (refereegranskat)abstract
- This study reviews assessment methods in DHM tools and explore the utilization of these methods in industry. Interviews with DHM users and ergonomics specialists within the Swedish automotive industry showed that simulations and following evaluations are almost solely based on static postures. Integrated evaluation tools in current DHM systems are seldom utilized; instead they use company specific evaluation methods. Both the review of current DHM tools and the interviews confirmed that there is an evident need for more time-dependant evaluation methods. The results are used to present a conceptual DHM module dealing with time-dependant ergonomics assessment.
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| 8. |
- Andersson, Henrik, et al.
(författare)
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Processing and Characterization of a MOS Type Tetra Lateral Position Sensitive Detector with Indium Tin Oxide Gate Contact
- 2008
-
Ingår i: IEEE Sensors Journal. - 1530-437X .- 1558-1748. ; 8:9-10, s. 1704-1709
-
Tidskriftsartikel (refereegranskat)abstract
- A 2-D tetra lateral position sensitive detector (PSD) based on the metal-oxide-semiconductor (MOS) principle has been manufactured and characterized. The active area of the device is 5 nun x 5 mm and the intention is to use the central 4 nun x 4 nun for low nonlinearity measurements. The gate contact is made of indium tin oxide (ITO) that is a degenerate electrically conducting semiconductor, which, in addition, is also transparent in the visible part of the spectrum. The use of a MOS structure results in a processing with no necessity to use implantation or diffusion in order to make the resistive p-layer as in a conventional p-n junction lateral effect PSD. Position measurements show good linearity in the middle 4 nun x 4 mm area. Within the middle 2.1 mm x 2.1 mm, the nonlinearity is within 1.7% of the active area with a position detection error of maximum 60 mu m. Measured MOS IV characteristics are compared to a level 3 spice model fit and show good agreement. The threshold voltage is determined to be -0.03 V. Responsivity measurements show a high sensitivity in the visible spectral region.
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| 9. |
- Bertilsson, Erik, et al.
(författare)
-
Assessment of manikin motions in IMMA
- 2012
-
Ingår i: Advances in applied human modeling and simulation. - Boca Raton : CRC Press. - 9781439870310 - 9781439870327 - 9780429061943 ; , s. 235-244
-
Bokkapitel (refereegranskat)abstract
- When evaluating human-machine interaction in a virtual environment using Digital human modelling (DHM) it is important to ensure that the predicted motions lie within the range of behavioural diversity for different people within a population. This paper presents a study in which a comparison is made between motions predicted by the DHM tool IMMA (Intelligently Moving Manikin) and motions from real humans stored in a motion database. Results show similar motions but the predicted motions were in total statistically significantly different compared to the motions performed by real persons. The differences are most likely due to the balance function and joint constraints that the IMMA tool uses for predicting motions. Differences can also be due to other factors, aside of body size, such as age, gender or strength that affects the movement behaviour.
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| 10. |
- Bertilsson, Erik, et al.
(författare)
-
Creation of the IMMA manikin with consideration of anthropometric diversity
- 2011
-
Ingår i: 21st International Conference on Production Research: Innovation in Product and Production, ICPR 2011; Stuttgart; Germany; 31 July 2011 through 4 August 2011. - : Fraunhofer Verlag. - 9783839602935 - 3839602939
-
Konferensbidrag (refereegranskat)abstract
- Digital human modelling (DHM) systems are used to simulate production processes and analyse the human-machine interaction, particularly at early development stages. Consideration of anthropometric variation is central in DHM simulations due to the necessity of ensuring intended accommodation levels. This paper describes the process of how digital human models are created and defined within the IMMA software. The process begins with the definition of a number of key measurements, which acts as the basis for the definition of several boundary manikins using a confidence ellipsoid methodology. These manikins represents the appropriate confidence region and hence the anthropometric diversity. Key measurements are then entered into regression equations to define the complete set of measurements for each manikin. These measurements are based on the appropriate ISO-standard. Finally, measurements are used to define the size and alignment of each segment in the biomechanical model of the manikin. The manikins are then used to automatically simulate and analyse human-machine interaction.
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| 11. |
- Bertilsson, Erik, et al.
(författare)
-
Digital Human Model Module and Work Process for Considering Anthropometric Diversity
- 2010
-
Ingår i: Proceedings of the 3rd Applied Human Factors and Ergonomics (AHFE) International Conference. - Louisville : AHFE International. - 9780979643545
-
Konferensbidrag (refereegranskat)abstract
- In digital human modelling (DHM), ergonomics evaluations are typically done with few human models. However, humans vary a lot in sizes and shapes. Therefore, few manikins can rarely ensure accommodation of an entire target population. Different approaches exist on how to consider anthropometric diversity. This paper reviews current DHM tools and clarify problems and opportunities when working with anthropometric diversity. The aim is to suggest functionality for a state of the art DHM module and work process for considering anthropometric diversity. The study is done by an analysis of some of the current DHM systems and by interviews of personnel at car companies about their way of working with anthropometric diversity. The study confirmed that critical production simulations are often done in early development stages with only one or a few human models. The reason for this is claimed to be time consuming processes, both at the creation of the human model but mainly when correctly positioning the model in the CAD environment. The development of a new method and work process for considering anthropometric diversity is suggested. Necessary features for such a module are that it shall be easy to use and not require expert knowledge about the consideration of anthropometric diversity. It shall also be configurable and transparent, in a sense that it should be possible to work with own anthropometric data and ergonomics evaluation standards. The module has to be flexible and have different entrances depending on the type of anthropometric problem being analyzed. An improved work method is expected to lead to faster and more correct analyses.
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| 12. |
- Bertilsson, Erik, et al.
(författare)
-
Digital Human Model Module and Work Process for Considering Anthropometric Diversity
- 2011. - 1
-
Ingår i: Advances in Applied Digital Human Modeling. - Boca Raton : CRC Press. - 9781439835128 - 9781439835111 - 9780429151842 ; , s. 568-577
-
Bokkapitel (refereegranskat)abstract
- In digital human modelling (DHM), ergonomics evaluations are typically done with few human models. However, humans vary a lot in sizes and shapes. Therefore, few manikins can rarely ensure accommodation of an entire target population. Different approaches exist on how to consider anthropometric diversity. This paper reviews current DHM tools and clarify problems and opportunities when working with anthropometric diversity. The aim is to suggest functionality for a state of the art DHM module and work process for considering anthropometric diversity. The study is done by an analysis of some of the current DHM systems and by interviews of personnel at car companies about their way of working with anthropometric diversity. The study confirmed that critical production simulations are often done in early development stages with only one or a few human models. The reason for this is claimed to be time consuming processes, both at the creation of the human model but mainly when correctly positioning the model in the CAD environment. The development of a new method and work process for considering anthropometric diversity is suggested. Necessary features for such a module are that it shall be easy to use and not require expert knowledge about the consideration of anthropometric diversity. It shall also be configurable and transparent, in a sense that it should be possible to work with own anthropometric data and ergonomics evaluation standards. The module has to be flexible and have different entrances depending on the type of anthropometric problem being analyzed. An improved work method is expected to lead to faster and more correct analyses.
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| 13. |
- Bertilsson, Erik, 1990-, et al.
(författare)
-
Low-Latency Parallel Hermitian Positive-Definite Matrix Inversion for Massive MIMO
- 2021
-
Ingår i: 2021 IEEE WORKSHOP ON SIGNAL PROCESSING SYSTEMS (SIPS 2021). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781665401449 - 9781665401456 ; , s. 23-28
-
Konferensbidrag (refereegranskat)abstract
- In this work, the effect of latency for three different positive definite matrix inversion algorithms when implemented on parallel and pipelined processing elements is considered. The work is motivated by the fact that in a massive MIMO system, matrix inversion needs to be performed between estimating the channels and producing the transmitted downlink signal, which means that the latency of the matrix inversion has a significant impact on the system performance. It is shown that, despite the algorithms having different complexity, all three algorithms can have the lowest latency for different number of processing elements and pipeline levels. Especially, in systems with many processing elements, the algorithm with the highest complexity has the lowest latency.
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| 14. |
- Bertilsson, Erik, et al.
(författare)
-
Multidimensional consideration of anthropometric diversity
- 2011
-
Ingår i: Proceedings of DHM, First International Symposium on Digital Human Modeling. - : Université Claude Bernard Lyon. - 9782953951509 ; , s. 1-6
-
Konferensbidrag (refereegranskat)abstract
- Boundary manikins, the concept of creating statistically extreme cases to accommodate a big part of the less extreme population has been known for decades. Despite this, many ergonomics simulations are done with few human models. This fact can be explained by the time consuming processes when working with many manikins in current digital human modelling (DHM) tools, but may also be a result of difficulty to understand how these manikins are calculated and defined. This paper focuses on the method of defining boundary manikins and how that functionality can be integrated into a DHM tool. Examples of boundary case methods in the literature often use Principal Component Analysis (PCA) which makes it possible to reduce the dimensions of the problem without much loss of the variance of the analysed data. Using PCA often demands some extent of manual analysis at the critical stage of reducing dimensions. This paper will explain a similar methodology for ceating boundary manikins from any number of variables, i.e. anthropometric variables chosen as key measurements. This method of creating a group of manikins is intended to be used in an automatic simulation feature in the IMMA software being developed in the associated research project. By using the method, a confidence region in the standardized space is created from eigenvectors and scaled eigenvalues of a correlation matrix. Boundary manikins are chosen at the ends of the axes of the enclosing confidence region, and one manikin of mean values is also added to the group of manikins. In the method presented here, the number of manikins created depends directly on the number of variables, which lead to the fact that the decision making of which key measurements to consider has to be done carefully to not create an overwhelming number of manikins. In comparison with one method using PCA, the method presented in this paper creates more manikins with a bigger difference in the max and min values of the chosen key measurements. If a limited number of cases are of crucial interest, then using PCA to reduce the dimensions of the problem is a good method to use. But if it is possible to create automated simulations the limitation of the number of manikins might not be so important. This will, though, depend heavily on the speed of the automated simulations.
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| 15. |
- Bertilsson, Erik, et al.
(författare)
-
Swedish engineering anthropometric web resource
- 2011
-
Ingår i: Proceedings of NES2011 September 18—21, 2011 Oulu, Finland. - Oulu : University of Oulu. - 9789514295416 ; , s. 442-446
-
Konferensbidrag (refereegranskat)abstract
- Anthropometry, the study of human measurements, is central in the design of products and workplaces. This paper describes how Swedish anthropometric data is made available through a web page (www.antropometri.se) intended to be used by designers and engineers when developing new products and workplaces. With the anthropometric web resource it is possible to get mean and standard deviation values, and to calculate percentile values, for a number of anthropometric measurements. Further functionality on the web page enables simultaneous consideration of several anthropometric measurements. The web page also contains guidelines for how to use anthropometric data depending on the design task at hand.
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| 16. |
- Bertilsson, Erik, et al.
(författare)
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Using experimental design to define boundary manikins
- 2012
-
Ingår i: Work. - : IOS Press. - 1051-9815 .- 1875-9270. ; 41, s. 4598-4605
-
Tidskriftsartikel (refereegranskat)abstract
- When evaluating human-machine interaction it is central to consider anthropometric diversity to ensure intended accommodation levels. A well-known method is the use of boundary cases where manikins with extreme but likely measurement combinations are derived by mathematical treatment of anthropometric data. The supposition by that method is that the use of these manikins will facilitate accommodation of the expected part of the total, less extreme, population. In literature sources there are differences in how many and in what way these manikins should be defined. A similar field to the boundary case method is the use of experimental design in where relationships between affecting factors of a process is studied by a systematic approach. This paper examines the possibilities to adopt methodology used in experimental design to define a group of manikins. Different experimental designs were adopted to be used together with a confidence region and its axes. The result from the study shows that it is possible to adapt the methodology of experimental design when creating groups of manikins. The size of these groups of manikins depends heavily on the number of key measurements but also on the type of chosen experimental design.
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| 17. |
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| 18. |
- Bertilsson, Kent, et al.
(författare)
-
Calculation of lattice heating in SiC RF power devices
- 2004
-
Ingår i: Solid-State Electronics. - : Elsevier BV. - 0038-1101 .- 1879-2405. ; 48:12, s. 1721-1725
-
Tidskriftsartikel (refereegranskat)abstract
- Silicon carbide MESFET devices are suitable for high-speed and high-power applications. In this paper we are studying thermal effects in 4H-SiC RF power devices. The simulations are based on a combination of 2D device simulations for the electrical transport, and 3D thermal simulations for the lattice heating. We show that the method gives good accuracy, efficiency, flexibility and capacity dealing with tasks, where a 2D coupled electrical-thermal simulation is not sufficient. We also present an improvement of Roschke and Schwierz mobility model, based on Monte Carlo simulations for the temperature dependencies of the mobility parameters beta and v(sat).
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| 19. |
- Bertilsson, Kent, et al.
(författare)
-
Monte Carlo simulation of vertical MESFETs in 2H, 4H and 6H-SiC
- 2001
-
Ingår i: Diamond and related materials. - 0925-9635 .- 1879-0062. ; 10:3-7, s. 1283-1286
-
Tidskriftsartikel (refereegranskat)abstract
- The 4H-SiC static induction transistor (SIT) is a very competitive device for high frequency and high power applications (3-6 GHz range). The large breakdown voltage and the high thermal conductivity of 4H-SiC allow transistors with extremely high current density at high voltages. The SIT transistor shows better output power capabilities but the unity current-gain frequency is lower compared to a MESFET device. In this work we show, using a very accurate numerical model, that a compromise between the features given by the SIT structure and the ordinary MESFET structure can be obtained using the vertical MESFET structure. The device dimension has been selected very aggressively to demonstrate the performance of an optimized technology. We also present results from drift-diffusion simulations of devices, using transport parameters obtained from the Monte Carlo simulation. The simulations indicate that 2H-SiC is superior to both 4H and 6H-SiC for vertical devices. For lateral devices, 2H-SiC is slightly faster compared to an identical 4H-SiC device
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| 20. |
- Bertilsson, Kent, et al.
(författare)
-
Optimization of 2H, 4H and 6H-SiC high-speed vertical MESFETs
- 2002
-
Ingår i: Diamond and related materials. - 0925-9635 .- 1879-0062. ; 11:3-6, s. 1254-1257
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Tidskriftsartikel (refereegranskat)abstract
- Silicon carbide vertical MESFET devices are well suited for high speed and high power electronic devices. In this work we have optimized the geometry of vertical MESFETs for microwave applications, using iterative two-dimensional simulations. Relevant parasitics are included in the simulations to investigate the performance of realistic devices. The state of the art device has f(T)=7 GHz and we show that vertical MESFETs fabricated with traditional technology are totally limited by parasitics. Two different approaches to reduce the parasitics in the vertical MESFET are proposed where f(T) increases significantly.
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| 21. |
- Bertilsson, Kent, et al.
(författare)
-
Optimization of 2H, 4H and 6H-SiC MESFETs for High Frequency Applications
- 2002
-
Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; 101, s. 75-77
-
Tidskriftsartikel (refereegranskat)abstract
- Silicon carbide MESFET devices are well suited for high speed, high power and high temperature electronics due to high saturation velocity, high critical electrical field, good thermal conductivity and large band-gap. Optimization of a high performance device demands a substantial number of numerical simulations, where several different design parameters have to be investigated thoroughly. In this work, we optimize the geometry of lateral MESFETs for maximal unity current-gain frequency (fT) using iterative 2-dimensional simulations. We also present a comparison of performance for individually optimized devices, realized with lithographic resolutions ranging from 0.2 to 2 μm in different SiC polytypes.
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| 22. |
- Bertilsson, Kent, 1973-
(författare)
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Simulation and Optimization of SiC Field Effect Transistors
- 2004
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Silicon Carbide (SiC) is a wide band-gap semiconductor material with excel-lent material properties for high frequency, high power and high temperature elec-tronics. In this work different SiC field-effect transistors have been studied using theoretical methods, with the focus on both the devices and the methods used. The rapid miniaturization of commercial devices demands better physical models than the drift-diffusion and hydrodynamic models most commonly used at present. The Monte Carlo method is the most accurate physical methods available and has been used in this work to study the performance in short-channel SiC field-effect devices. The drawback of the Monte-Carlo method is the computational power required and it is thus not well suited for device design where the layout requires to be optimized for best device performance. One approach to reduce the simulation time in the Monte Carlo method is to use a time-domain drift-diffusion model in contact and bulk regions of the device. In this work, a time-domain drift-diffusion model is implemented and verified against commercial tools and would be suitable for inclusion in the Monte-Carlo device simulator framework. Device optimization is traditionally performed by hand, changing device pa-rameters until sufficient performance is achieved. This is very time consuming work without any guarantee of achieving an optimal layout. In this work a tool is developed, which automatically changes device layout until optimal device per-formance is achieved. Device optimization requires hundreds of device simulations and thus it is essential that computationally efficient methods are used. One impor-tant physical process for RF power devices is self heating. Self heating can be fairly accurately modeled in two dimensions but this will greatly reduce the computa-tional speed. For realistic influence self heating must be studied in three dimensions and a method is developed using a combination of 2D electrical and 3D thermal simulations. The accuracy is much improved by using the proposed method in comparison to a 2D coupled electro/thermal simulation and at the same time offers greater efficiency. Linearity is another very important issue for RF power devices for telecommunication applications. A method to predict the linearity is imple-mented using nonlinear circuit simulation of the active device and neighboring passive elements.
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| 23. |
- Bertilsson, Kent, et al.
(författare)
-
Simulation of a low atmospheric-noise modified four-quadrant position sensitive detector
- 2001
-
Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 466:1, s. 183-187
-
Tidskriftsartikel (refereegranskat)abstract
- A modified four-quadrant position sensitive detector (PSD) is developed. This structure is less sensitive to atmospheric turbulence that is a major drawback with the traditional four-quadrant detector. The inter-electrode resistance is as high as for the four-quadrant detector, which is an advantage compared to the lateral effect PSD. The linearity for the modified four-quadrant detector is good in the whole active range of sensing. The structures are limited to small sensing areas with well focused beams and are suitable for use in detectors up to 1 mm in size.
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| 24. |
- Bertilsson, Kent, et al.
(författare)
-
Simulation of anisotropic Breakdown in 4H-SiC Diodes
- 2000
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Ingår i: IEEE Workshop on Computers in Power Electronics. - : IEEE. ; , s. 118-120
-
Konferensbidrag (refereegranskat)abstract
- The breakdown characteristics of two-dimensional 4H-SiC diode structures have been studied using an anisotropic drift-diffusion model. The degree of anisotropy was estimated from recent full band Monte Carlo simulations. Identical diode structures have previously been used in the literature to measure the hole impact ionization coefficients of 4H-SiC. The reported measurements from different research groups show large differences in the impact ionization coefficients. Our numerical simulations show that the differences in these measurements can be explained by the difference in device geometry used by the research teams if one considers an anisotropic impact ionization process. This indicates that it is very important to consider anisotropic impact ionization in design and characterization of 4H-SiC power devices.
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| 25. |
- Bertilsson, Kent, et al.
(författare)
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The Effect of Different Transport Models in Simulation of High Frequency 4H-SiC and 6H-SiC Vertical MESFETs
- 2001
-
Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 45:5, s. 645-653
-
Tidskriftsartikel (refereegranskat)abstract
- A full band Monte Carlo (MC) study of the high frequency performance of a 4H-SiC Short channel vertical MESFET is presented. The MC model used is based on data from a full potential band structure calculation using the local density approximation to the density functional theory. The MC results have been compared with simulations using state of the art drift-diffusion and hydrodynamic transport models. Transport parameters such as mobility, saturation velocity and energy relaxation time are extracted from MC simulations
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| 26. |
- Bertilsson, Kent, et al.
(författare)
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The power of using automatic device optimization, based on iterative device simulation, in design of high-performance devices
- 2004
-
Ingår i: Solid-State Electronics. - : Elsevier BV. - 0038-1101 .- 1879-2405. ; 48:10-11, s. 1721-1725
-
Tidskriftsartikel (refereegranskat)abstract
- An automatic optimization tool for semiconductor devices based on iterative device simulations is developed. The tool is used for optimization of different kinds of semiconductor devices using various performance measures. High performance optimization algorithms, both local and global, are used to achieve an efficient design in shortest possible time. In this paper the effects of different optimization algorithms, performance measures, and number of variables in the optimization are studied. Both the computational efficiency and the devices achieved with different performance measures are studied. We give a demonstration of the usefulness of this method in a comparison between different device topologies, which have been optimized for best performance.
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| 27. |
- Bertilsson, Kent, et al.
(författare)
-
The power of using automatic device optimization, based on iterative device simulations, in design of high-performance devices
- 2003
-
Ingår i: 2003 International Semiconductor Device Research Symposium, ISDRS 2003 - Proceedings. - 0780381394 - 9780780381391 ; , s. 152-153
-
Konferensbidrag (refereegranskat)abstract
- Device design is a time consuming work, where the influence of many design parameters has to be investigated carefully. In advanced devices optimal performance is often achieved taking multiple trade-off into consideration, and manual device optimization is often insufficient. In this paper we present the feasibility of using device optimization for design on electronic devices. An optimization tool is developed, which runs device simulations and automatically changes the design parameters, searching for optimal performance according to a specified performance measure. This has been shown to be a very time and cost efficient way for device design, as the search for optimal performance is fuily automatic working in a systematic way 24 hours 7 days a week. From an industrial point of view this is very important as it can reduce the evaluation and optimization cost for new devices considerably. It is impossible to give a fair comparison between different devices unless these are designed to give optimal performance. We give a demonstration of the usefulness of this method in a comparison between different device topologies which individually have been optimized for best performance.
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| 28. |
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| 29. |
- Bertilsson, S., et al.
(författare)
-
Lithium-ion battery electrolyte emissions analyzed by coupled thermogravimetric/Fourier-transform infrared spectroscopy
- 2017
-
Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753 .- 1873-2755. ; 365, s. 446-455
-
Tidskriftsartikel (refereegranskat)abstract
- In the last few years the use of Li-ion batteries has increased rapidly, powering small as well as large applications, from electronic devices to power storage facilities. The Li-ion battery has, however, several safety issues regarding occasional overheating and subsequent thermal runaway. During such episodes, gas emissions from the electrolyte are of special concern because of their toxicity, flammability and the risk for gas explosion. In this work, the emissions from heated typical electrolyte components as well as from commonly used electrolytes are characterized using FT-IR spectroscopy and FT-IR coupled with thermogravimetric (TG) analysis, when heating up to 650 degrees C. The study includes the solvents EC, PC, DEC, DMC and EA in various single, binary and ternary mixtures with and without the LiPF6 salt, a commercially available electrolyte, (LP71), containing EC, DEC, DMC and LiPF6 as well as extracted electrolyte from a commercial 6.8 Ah Li-ion cell. Upon thermal heating, emissions of organic compounds and of the toxic decomposition products hydrogen fluoride (HF) and phosphoryl fluoride (POF3) were detected. The electrolyte and its components have also been extensively analyzed by means of infrared spectroscopy for identification purposes.
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| 30. |
- Bravo, Andrea G., et al.
(författare)
-
Methanogens and iron-reducing bacteria : the overlooked members of mercury-methylating microbial communities in boreal lakes
- 2018
-
Ingår i: Applied and Environmental Microbiology. - : American Society for Microbiology. - 0099-2240 .- 1098-5336. ; 84:23
-
Tidskriftsartikel (refereegranskat)abstract
- ABSTRACT: Methylmercury is a potent human neurotoxin which biomagnifies in aquatic food webs. Although anaerobic microorganisms containing the hgcA gene potentially mediate the formation of methylmercury in natural environments, the diversity of these mercury-methylating microbial communities remains largely unexplored. Previous studies have implicated sulfate-reducing bacteria as the main mercury methylators in aquatic ecosystems. In the present study, we characterized the diversity of mercury-methylating microbial communities of boreal lake sediments using high-throughput sequencing of 16S rRNA and hgcA genes. Our results show that in the lake sediments, Methanomicrobiales and Geobacteraceae also represent abundant members of the mercury-methylating communities. In fact, incubation experiments with a mercury isotopic tracer and molybdate revealed that only between 38% and 45% of mercury methylation was attributed to sulfate reduction. These results suggest that methanogens and iron-reducing bacteria may contribute to more than half of the mercury methylation in boreal lakes.IMPORTANCE: Despite the global awareness that mercury, and methylmercury in particular, is a neurotoxin to which millions of people continue to be exposed, there are sizable gaps in the understanding of the processes and organisms involved in methylmercury formation in aquatic ecosystems. In the present study, we shed light on the diversity of the microorganisms responsible for methylmercury formation in boreal lake sediments. All the microorganisms identified are associated with the processing of organic matter in aquatic systems. Moreover, our results show that the well-known mercury-methylating sulfate-reducing bacteria constituted only a minor portion of the potential mercury methylators. In contrast, methanogens and iron-reducing bacteria were important contributors to methylmercury formation, highlighting their role in mercury cycling in the environment.
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| 31. |
- Bravo, Andrea Garcia, et al.
(författare)
-
Methanogens and Iron-Reducing Bacteria : the Overlooked Members of Mercury-Methylating Microbial Communities in Boreal Lakes
- 2018
-
Ingår i: Applied and Environmental Microbiology. - 0099-2240 .- 1098-5336. ; 84:23
-
Tidskriftsartikel (refereegranskat)abstract
- Methylmercury is a potent human neurotoxin which biomagnifies in aquatic food webs. Although anaerobic microorganisms containing the hgcA gene potentially mediate the formation of methylmercury in natural environments, the di- versity of these mercury-methylating microbial communities remains largely unex- plored. Previous studies have implicated sulfate-reducing bacteria as the main mer- cury methylators in aquatic ecosystems. In the present study, we characterized the diversity of mercury-methylating microbial communities of boreal lake sediments us- ing high-throughput sequencing of 16S rRNA and hgcA genes. Our results show that in the lake sediments, Methanomicrobiales and Geobacteraceae also represent abun- dant members of the mercury-methylating communities. In fact, incubation experi- ments with a mercury isotopic tracer and molybdate revealed that only between 38% and 45% of mercury methylation was attributed to sulfate reduction. These re- sults suggest that methanogens and iron-reducing bacteria may contribute to more than half of the mercury methylation in boreal lakes.
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| 32. |
- Bravo, Andrea G., et al.
(författare)
-
Molecular composition of organic matter controls methylmercury formation in boreal lakes
- 2017
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- A detailed understanding of the formation of the potent neurotoxic methylmercury is needed to explain the large observed variability in methylmercury levels in aquatic systems. While it is known that organic matter interacts strongly with mercury, the role of organic matter composition in the formation of methylmercury in aquatic systems remains poorly understood. Here we show that phytoplankton-derived organic compounds enhance mercury methylation rates in boreal lake sediments through an overall increase of bacterial activity. Accordingly, in situ mercury methylation defines methylmercury levels in lake sediments strongly influenced by planktonic blooms. In contrast, sediments dominated by terrigenous organic matter inputs have far lower methylation rates but higher concentrations of methylmercury, suggesting that methylmercury was formed in the catchment and imported into lakes. Our findings demonstrate that the origin and molecular composition of organic matter are critical parameters to understand and predict methylmercury formation and accumulation in boreal lake sediments.
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| 33. |
- Cabrol, Léa, et al.
(författare)
-
Redox gradient shapes the abundance and diversity of mercury-methylating microorganisms along the water column of the Black Sea
- 2023
-
Ingår i: mSystems. - : American Society for Microbiology. - 2379-5077. ; 8:4
-
Tidskriftsartikel (refereegranskat)abstract
- In the global context of seawater deoxygenation triggered by climate change and anthropogenic activities, changes in redox gradients impacting biogeochemical transformations of pollutants, such as mercury, become more likely. Being the largest anoxic basin worldwide, with high concentrations of the potent neurotoxic methylmercury (MeHg), the Black Sea is an ideal natural laboratory to provide new insights about the link between dissolved oxygen concentration and hgcAB gene-carrying (hgc+) microorganisms involved in the formation of MeHg. We combined geochemical and microbial approaches to assess the effect of vertical redox gradients on abundance, diversity, and metabolic potential of hgc+ microorganisms in the Black Sea water column. The abundance of hgcA genes [congruently estimated by quantitative PCR (qPCR) and metagenomics] correlated with MeHg concentration, both maximal in the upper part of the anoxic water. Besides the predominant Desulfobacterales, hgc+ microorganisms belonged to a unique assemblage of diverse—previously underappreciated—anaerobic fermenters from Anaerolineales, Phycisphaerae (characteristic of the anoxic and sulfidic zone), Kiritimatiellales, and Bacteroidales (characteristic of the suboxic zone). The metabolic versatility of Desulfobacterota differed from strict sulfate reduction in the anoxic water to reduction of various electron acceptors in the suboxic water. Linking microbial activity and contaminant concentration in environmental studies is rare due to the complexity of biological pathways. In this study, we disentangle the role of oxygen in shaping the distribution of Hg-methylating microorganisms consistently with MeHg concentration, and we highlight their taxonomic and metabolic niche partitioning across redox gradients, improving the prediction of the response of marine communities to the expansion of oxygen-deficient zones. IMPORTANCE Methylmercury (MeHg) is a neurotoxin detected at high concentrations in certain marine ecosystems, posing a threat to human health. MeHg production is mainly mediated by hgcAB gene-carrying (hgc+) microorganisms. Oxygen is one of the main factors controlling Hg methylation; however, its effect on the diversity and ecology of hgc+ microorganisms remains unknown. Under the current context of seawater deoxygenation, mercury cycling is expected to be disturbed. Here, we show the strong effect of oxygen gradients on the distribution of potential Hg methylators. In addition, we show for the first time the significant contribution of a unique assemblage of potential fermenters from Anaerolineales, Phycisphaerae, and Kiritimatiellales to Hg methylation, stratified in different redox niches along the Black Sea gradient. Our results considerably expand the known taxonomic diversity and ecological niches prone to the formation of MeHg and contribute to better apprehend the consequences of oxygen depletion in seawater.
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| 34. |
- Capo, Eric, et al.
(författare)
-
A consensus protocol for the recovery of mercury methylation genes from metagenomes
- 2023
-
Ingår i: Molecular Ecology Resources. - : John Wiley & Sons. - 1755-098X .- 1755-0998. ; 23:1, s. 190-204
-
Tidskriftsartikel (refereegranskat)abstract
- Mercury (Hg) methylation genes (hgcAB) mediate the formation of the toxic methylmercury and have been identified from diverse environments, including freshwater and marine ecosystems, Arctic permafrost, forest and paddy soils, coal-ash amended sediments, chlor-alkali plants discharges and geothermal springs. Here we present the first attempt at a standardized protocol for the detection, identification and quantification of hgc genes from metagenomes. Our Hg-cycling microorganisms in aquatic and terrestrial ecosystems (Hg-MATE) database, a catalogue of hgc genes, provides the most accurate information to date on the taxonomic identity and functional/metabolic attributes of microorganisms responsible for Hg methylation in the environment. Furthermore, we introduce "marky-coco", a ready-to-use bioinformatic pipeline based on de novo single-metagenome assembly, for easy and accurate characterization of hgc genes from environmental samples. We compared the recovery of hgc genes from environmental metagenomes using the marky-coco pipeline with an approach based on coassembly of multiple metagenomes. Our data show similar efficiency in both approaches for most environments except those with high diversity (i.e., paddy soils) for which a coassembly approach was preferred. Finally, we discuss the definition of true hgc genes and methods to normalize hgc gene counts from metagenomes.
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| 35. |
- Capo, Eric, et al.
(författare)
-
Deltaproteobacteria andSpirochaetes-Like Bacteria AreAbundant Putative MercuryMethylators in Oxygen-DeficientWater and Marine Particles in theBaltic Sea
- 2020
-
Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; , s. 1-11
-
Tidskriftsartikel (refereegranskat)abstract
- Methylmercury (MeHg), a neurotoxic compound biomagnifying in aquatic food webs, can be a threat to human health via fish consumption. However, the compositionand distribution of the microbial communities mediating the methylation of mercury (Hg) to MeHg in marine systems remain largely unknown. In order to fill this knowledge gap, we used the Baltic Sea Reference Metagenome (BARM) dataset to study the abundance and distribution of the genes involved in Hg methylation (the hgcAB gene cluster). We determined the relative abundance of the hgcAB genes and their taxonomic identity in 81 brackish metagenomes that cover spatial,seasonal and redox variability in the Baltic Sea water column. The hgcAB genes were predominantly detected in anoxic water, but some hgcAB genes were alsodetected in hypoxic and normoxic waters. Phylogenetic analysis identified putative Hg methylators within Deltaproteobacteria, in oxygen-deficient water layers, but also Spirochaetes-like and Kiritimatiellaeota-like bacteria. Higher relative quantities of hgcAB genes were found in metagenomes from marine particles compared to free-living communities in anoxic water, suggesting that such particles are hotspot habitats for Hg methylators in oxygen-depleted seawater. Altogether, our work unveils the diversityof the microorganisms with the potential to mediate MeHg production in the BalticSea and pinpoint the important ecological niches for these microorganisms within themarine water column.
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| 36. |
- Capo, Eric, et al.
(författare)
-
Expression Levels of hgcAB Genes and Mercury Availability Jointly Explain Methylmercury Formation in Stratified Brackish Waters
- 2022
-
Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 56:18, s. 13119-13130
-
Tidskriftsartikel (refereegranskat)abstract
- Neurotoxic methylmercury (MeHg) is formed by microbial methylation of inorganic divalent Hg (Hg-II) and constitutes severe environmental and human health risks. The methylation is enabled by hgcA and hgcB genes, but it is not know nif the associated molecular-level processes are rate-limiting or enable accurate prediction of MeHg formation in nature. In this study, we investigated the relationships between hgc genes and MeHg across redox-stratified water columns in the brackish Baltic Sea. We showed, for the first time, that hgc transcript abundance and the concentration of dissolved Hg-II-sulfide species were strong predictors of both the Hg-II methylation rate and MeHg concentration, implying their roles as principal joint drivers of MeHg formation in these systems. Additionally, we characterized the metabolic capacities of hgc(+) microorganisms by reconstructing their genomes from metagenomes (i.e., hgc(+) MAGs), which highlighted the versatility of putative Hg-II methylators in the water column of the Baltic Sea. In establishing relationships between hgc transcripts and the Hg-II methylation rate, we advance the fundamental understanding of mechanistic principles governing MeHg formation in nature and enable refined predictions of MeHg levels in coastal seas in response to the accelerating spread of oxygen-deficientzones.
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| 37. |
- Capo, Eric, et al.
(författare)
-
Oxygen-deficient water zones in the Baltic Sea promote uncharacterized Hg methylating microorganisms in underlying sediments
- 2022
-
Ingår i: Limnology and Oceanography. - : Wiley. - 1939-5590 .- 0024-3590. ; 67:1, s. 135-146
-
Tidskriftsartikel (refereegranskat)abstract
- Human-induced expansion of oxygen-deficient zones can have dramatic impacts on marine systems and its resident biota. One example is the formation of the potent neurotoxic methylmercury (MeHg) that is mediated by microbial methylation of inorganic divalent Hg (HgII) under oxygen-deficient conditions. A negative consequence of the expansion of oxygen-deficient zones could be an increase in MeHg production due to shifts in microbial communities in favor of microorganisms methylating Hg. There is, however, limited knowledge about Hg-methylating microbes, i.e., those carrying hgc genes critical for mediating the process, from marine sediments. Here, we aim to study the presence of hgc genes and transcripts in metagenomes and metatranscriptomes from four surface sediments with contrasting concentrations of oxygen and sulfide in the Baltic Sea. We show that potential Hg methylators differed among sediments depending on redox conditions. Sediments with an oxygenated surface featured hgc-like genes and transcripts predominantly associated with uncultured Desulfobacterota (OalgD group) and Desulfobacterales (including Desulfobacula sp.) while sediments with a hypoxic-anoxic surface included hgc-carrying Verrucomicrobia, unclassified Desulfobacterales, Desulfatiglandales, and uncharacterized microbes. Our data suggest that the expansion of oxygen-deficient zones in marine systems may lead to a compositional change of Hg-methylating microbial groups in the sediments, where Hg methylators whose metabolism and biology have not yet been characterized will be promoted and expand.
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| 38. |
- Dubaric, Ervin, et al.
(författare)
-
Simulations of Submicron MOSFETs in 2H, 4H and 6H-SiC
- 2002
-
Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; 101, s. 14-17
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present numerical studies of the high frequency performance of a submicron MOSFET in 2H-, 4H- and 6H-SiC. The studies are based on simulations where commercial two-dimensional drift-diffusion and hydrodynamic carrier transport models have been used. The results have been compared with those obtained from full band Monte Carlo simulations. The Monte Carlo carrier transport model is based on data from a full potential band structure calculation using the Local Density Approximation to the Density Functional Theory. In 6H-SiC the bulk transport properties in the direction perpendicular to the c-axis, are slightly lower than in 2H- and 4H-SiC. However, in the direction parallel to the c-axis the transport properties are considerably less favourable than in the other two polytypes. The effects of these differences, on surface mobility device performance and carrier energy, have been studied.
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| 39. |
- Eklöf, Karin, et al.
(författare)
-
Formation of mercury methylation hotspots as a consequence of forestry operations
- 2018
-
Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 613-614, s. 1069-1078
-
Tidskriftsartikel (refereegranskat)abstract
- Earlier studies have shown that boreal forest logging can increase the concentration and export of methylmercury (MeHg) in stream runoff. Here we test whether forestry operations create soil environments of high MeHg net formation associated with distinct microbial communities. Furthermore, we test the hypothesis that Hg methylation hotspots are more prone to form after stump harvest than stem-only harvest, because of more severe soil compaction and soil disturbance. Concentrations of MeHg, percent MeHg of total Hg (THg), and bacterial community composition were determined at 200 soil sampling positions distributed across eight catchments. Each catchment was either stem-only harvested (n = 3), stem-and stump-harvested (n = 2) or left undisturbed (n = 3). In support of our hypothesis, higher MeHg to THg ratios was observed in one of the stump-harvested catchments. While the effects of natural variation could not be ruled out, we noted that most of the highest % MeHg was observed in water-filled cavities created by stump removal or driving damage. This catchment also featured the highest bacterial diversity and highest relative abundance of bacterial families known to include Hg methylators. We propose that water-logged and disturbed soil environments associated with stump harvest can favor methylating microorganisms, which also enhance MeHg formation.
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| 40. |
- Escaned, Javier, et al.
(författare)
-
Safety of the Deferral of Coronary Revascularization on the Basis of Instantaneous Wave-Free Ratio and Fractional Flow Reserve Measurements in Stable Coronary Artery Disease and Acute Coronary Syndromes
- 2018
-
Ingår i: JACC. - : Elsevier. - 1936-8798 .- 1876-7605. ; 11:15, s. 1437-1449
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES The aim of this study was to investigate the clinical outcomes of patients deferred from coronary revascularization on the basis of instantaneous wave-free ratio (iFR) or fractional flow reserve (FFR) measurements in stable angina pectoris (SAP) and acute coronary syndromes (ACS). BACKGROUND Assessment of coronary stenosis severity with pressure guidewires is recommended to determine the need for myocardial revascularization. METHODS The safety of deferral of coronary revascularization in the pooled per-protocol population (n = 4,486) of the DEFINE-FLAIR (Functional Lesion Assessment of Intermediate Stenosis to Guide Revascularisation) and iFR-SWEDEHEART (Instantaneous Wave-Free Ratio Versus Fractional Flow Reserve in Patients With Stable Angina Pectoris or Acute Coronary Syndrome) randomized clinical trials was investigated. Patients were stratified according to revascularization decision making on the basis of iFR or FFR and to clinical presentation (SAP or ACS). The primary endpoint was major adverse cardiac events (MACE), defined as the composite of all-cause death, nonfatal myocardial infarction, or unplanned revascularization at 1 year. RESULTS Coronary revascularization was deferred in 2,130 patients. Deferral was performed in 1,117 patients (50%) in the iFR group and 1,013 patients (45%) in the FFR group (p < 0.01). At 1 year, the MACE rate in the deferred population was similar between the iFR and FFR groups (4.12% vs. 4.05%; fully adjusted hazard ratio: 1.13; 95% confidence interval: 0.72 to 1.79; p = 0.60). A clinical presentation with ACS was associated with a higher MACE rate compared with SAP in deferred patients (5.91% vs. 3.64% in ACS and SAP, respectively; fully adjusted hazard ratio: 0.61 in favor of SAP; 95% confidence interval: 0.38 to 0.99; p = 0.04). CONCLUSIONS Overall, deferral of revascularization is equally safe with both iFR and FFR, with a low MACE rate of about 4%. Lesions were more frequently deferred when iFR was used to assess physiological significance. In deferred patients presenting with ACS, the event rate was significantly increased compared with SAP at 1 year. (C) 2018 The Authors. Published by Elsevier on behalf of the American College of Cardiology Foundation.
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| 41. |
- Gustafsson, Oscar, 1973-, et al.
(författare)
-
Approximate Neumann Series or Exact Matrix Inversion for Massive MIMO? (Invited Paper)
- 2017
-
Ingår i: Proceedings 2017 IEEE 24th Symposium on Computer Arithmetic (ARITH), London, UK, 24-26 July 2017. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538619650 - 9781538619643 - 9781538619667 ; , s. 62-63
-
Konferensbidrag (refereegranskat)abstract
- Approximate matrix inversion based on Neumann series has seen a recent increased interest motivated by massive MIMO systems. There, the matrices are in many cases diagonally dominant, and, hence, a reasonable approximation can be obtained within a few iterations of a Neumann series. In this work, we clarify that the complexity of exact methods are about the same as when three terms are used for the Neumann series, so in this case, the complexity is not lower as often claimed. The second common argument for Neumann series approximation, higher parallelism, is indeed correct. However, in most current practical use cases, such a high degree of parallelism is not required to obtain a low latency realization. Hence, we conclude that a careful evaluation, based on accuracy and latency requirements must be performed and that exact matrix inversion is in fact viable in many more cases than the current literature claims.
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| 42. |
- Hatta, Fazleen H M, et al.
(författare)
-
Differences in CYP2C9 Genotype and Enzyme Activity Between Swedes and Koreans of Relevance for Personalized Medicine : Role of Ethnicity, Genotype, Smoking, Age, and Sex
- 2015
-
Ingår i: Omics. - : Mary Ann Liebert Inc. - 1536-2310 .- 1557-8100. ; 19:6, s. 346-353
-
Tidskriftsartikel (refereegranskat)abstract
- Global personalized medicine demands the characterization of person-to-person and between-population differences in drug pharmacokinetics and pharmacodynamics. CYP2C9 pharmacokinetic pathway is subject to modulation by both genetic and environmental factors. CYP2C9 genotype-based dose recommendations (e.g., for warfarin) is advocated. However, the overall contribution of genotype for variation in enzyme activity may differ between populations. We evaluated the importance of ethnicity, genotype, smoking, body weight, age, and sex for CYP2C9 enzyme activity. CYP2C9 genotype and phenotype was determined in 148 Swedes and 146 Koreans using losartan as a probe. CYP2C9 enzyme activity was assessed using urinary losartan/metabolite E-3174 ratio. The frequency of CYP2C9 defective variant alleles (*2 and *3) was significantly higher in Swedes (10.8% and 12.5%) than in Koreans (0% and 5.8%). In matched genotypes, CYP2C9 enzyme activity was significantly lower in Swedes compared to Koreans (p<0.0001). In a univariate analysis, age, weight, ethnicity, genotype, and smoking were significant predictors of CYP2C9 phenotype. A stepwise multivariate analysis indicated ethnicity, genotype, and smoking remained as significant predictors of CYP2C9 enzyme activity, accounting for 50% of the total variance. In both study populations, CYP2C9 genotype was a significant predictor of CYP2C9 enzyme activity, but its contribution in explaining the total variance was lower in Koreans (26.6%) than Swedes (40%). In conclusion, we report significantly lower CYP2C9 enzyme activity in Swedes compared to Koreans, partly but not exclusively due to CYP2C9 pharmacogenetic variations. Ethnicity and environment factors need to be considered together with genotype for population-specific dose optimization and global personalized medicine.
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| 43. |
- Herrero Ortega, Sonia, et al.
(författare)
-
High methylmercury formation in ponds fueled by fresh humic and algal derived organic matter
- 2018
-
Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 63, s. S44-S53
-
Tidskriftsartikel (refereegranskat)abstract
- Neurotoxic methylmercury causes adverse effects to ecosystem viability and human health. Previous studies have revealed that ponding alters natural organic matter (NOM) composition and increase methylmercury concentrations in rivers, especially in the first years after flooding. Here, we investigate the influence of NOM composition (i.e., sources and degradation status) on mercury methylation rate constants in nine boreal beaver ponds of different ages across Sweden. We show that increased methylmercury concentrations in surface waters is a consequence of enhanced mercury methylation in the pond sediments. Moreover, our results reveal that during the first years after the initial flooding, mercury methylation rates are fueled by the amount of fresh humic substances released from the flooded soils and by an increased production of algal-derived NOM triggered by enhanced nutrient availability. Our findings indicate that impoundment-induced changes in NOM composition control mercury methylation processes, causing the raise in MeHg levels in ponds.
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| 44. |
- Hjelm, Mats, et al.
(författare)
-
Full Band Monte Carlo Study of Bulk and Surface Transport Properties in 4H and 6H-SiC
- 2001
-
Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 184:1-4, s. 194-198
-
Tidskriftsartikel (refereegranskat)abstract
- The bulk and surface electron transport properties of the 4H and 6H polytypes of silicon carbide (SiC) are studied using a full band Monte Carlo (MC) program. The model for the electrons is based on data from a full potential band structure calculation using the density functional theory (DFT) in the local density approximation (LDA). Both SiC polytypes have anisotropic transport properties, but the degree and characteristics of the anisotropy is different. In this study, we show how the anisotropy affects the bulk mobility for intermediate angles between the crystal axis and the plane perpendicular to it. Simulations of surface transport properties have also been performed for semiconductor-interface angles up to 15 degrees from the plane perpendicular to the c-axis. We present results for surface mobility and velocity as a function of the electric field component parallel to the interface plane. In the surface mobility simulations, a semi-empirical model for the semiconductor-insulator interface has been used, where it is assumed that the electrons are reflected in two perpendicular planes.
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| 45. |
- Hu, Haiyan, et al.
(författare)
-
Shifts in mercury methylation across a peatland chronosequence : From sulfate reduction to methanogenesis and syntrophy
- 2020
-
Ingår i: Journal of Hazardous Materials. - : Elsevier. - 0304-3894 .- 1873-3336. ; 387
-
Tidskriftsartikel (refereegranskat)abstract
- Peatlands are globally important ecosystems where inorganic mercury is converted to bioaccumulating and highly toxic methylmercury, resulting in high risks of methylmercury exposure in adjacent aquatic ecosystems. Although biological mercury methylation has been known for decades, there is still a lack of knowledge about the organisms involved in mercury methylation and the drivers controlling their methylating capacity. In order to investigate the metabolisms responsible for mercury methylation and methylmercury degradation as well as the controls of both processes, we studied a chronosequence of boreal peatlands covering fundamentally different biogeochemical conditions. Potential mercury methylation rates decreased with peatland age, being up to 53 times higher in the youngest peatland compared to the oldest. Methylation in young mires was driven by sulfate reduction, while methanogenic and syntrophic metabolisms became more important in older systems. Demethylation rates were also highest in young wetlands, with a gradual shift from biotic to abiotic methylmercury degradation along the chronosequence. Our findings reveal how metabolic shifts drive mercury methylation and its ratio to demethylation as peatlands age.
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| 46. |
- Högberg, Dan, et al.
(författare)
-
A basic step towards increased accommodation level accuracy when using DHM tools
- 2011
-
Ingår i: Proceedings of DHM, First International Symposium on Digital Human Modeling. - : Université Claude Bernard Lyon. - 9782953951509 ; , s. 1-6
-
Konferensbidrag (refereegranskat)abstract
- The paper addresses the need to consider anthropometric diversity in design and suggests a basic approach for the simultaneous consideration of variance in two key dimensions. This as a basic step from the common, but in many cases poor, approach to use univariate percentile data in design. The bivariate method described can be applied when utilising DHM tools for design in that key dimension values for extreme but likely anthropometric measurement combinations are calculated and entered as input data when representative manikins are defined. The mathematical procedure is described and the outcome of the method is compared to a typical percentile based approach, indicating more accurate accommodation levels being reached by the proposed method. The method is to be seen as a simple method to be used for basic design problems where variance in few anthropometric dimensions are to be considered simultaneously, and not as an alternative for more advanced multivariate methods. The paper takes a pragmatic standpoint, directing its message towards practitioners using DHM tools for design purposes.
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| 47. |
- Högberg, Dan, et al.
(författare)
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A pragmatic approach to define anthropometric boundary manikins for multiple populations
- 2012
-
Ingår i: NES2012 Proceedings, Saltsjöbaden, Sweden, August 19-22, 2012. - Stockholm : KTH Royal Institute of Technology. - 9789163711503
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Konferensbidrag (refereegranskat)abstract
- The paper addresses the call for methods that can assist designers to consider anthropometric diversity when designing products or workstations, and hence formulate more sustainable design solutions. A basic method for the definition of boundary manikins for bivariate design problems and combined populations is described, exemplified and evaluated. The method can be used for defining virtual test groups when using digital human modelling tools for evaluating anthropometry related aspects of human-product interfaces at early design phases. It can also be used to indentify persons with certain anthropometry to build up test groups for performing physical tests.
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| 48. |
- Jingying, Xu, 1984-, et al.
(författare)
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Mercury methylating microbial communities in boreal wetlands
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Understanding the formation of the potent neurotoxic methylmercury (MeHg) is a major concern due to its threats to wildlife and human health. As boreal wetlands play a crucial role for Hg cycling on a global scale, it is crucial to understand the biogeochemical processes involved in MeHg formation in this landscape. A strategy combining high-throughput hgcA amplicon sequencing with molecular barcoding was used to revealed diverse clades of Hg(II) methylators in a wide range of wetland soils. Our results confirms a predominant role of Deltaproteobacteria, and in particular Geobacteraceae, as important Hg(II) methylators in boreal wetland soils. Firmicutes, and in particular Ruminococcaceae, were also abundant members of the Hg(II) methylating microbial communities. Our survey highlight the importance of nutrient status for the shaping of Hg(II) methylating communities across the four wetlands and reveal that water content and prevailing redox states are key factors determining the local variation in Hg(II) methylating community composition within individual wetlands. Also, our study suggests that high nutrient levels linked to low redox potential seemed to favour Hg(II) methylating methanogens within the Methanoregulaceae. Our findings expand the current knowledge on the Hg(II) methylating microbial community composition in wetland soils and the geochemical factors underpinning spatial heterogeity in such communities.
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| 49. |
- Jingying, Xu, 1984-, et al.
(författare)
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Mercury methylating microbial communities of boreal forest soils
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- The formation of the potent neurotoxic methylmercury (MeHg) is a microbially mediated process that has raised much concern because MeHg poses threats to wildlife and human health. Since boreal forest soils can be a source of MeHg in aquatic networks, it is crucial to understand the biogeochemical processes involved in the formation of this pollutant. High-throughput sequencing of 16S rRNA and the mercury methyltransferase, hgcA, combined with geochemical characterisation of soils, were used to determine the microbial populations contributing to MeHg formation in forest soils across Sweden. The hgcA sequences obtained were distributed among diverse clades, including Proteobacteria, Firmicutes, and Methanomicrobia, with Deltaproteobacteria, particularly Geobacteraceae, dominating the libraries across all soils examined. Our results also suggest that MeHg formation is linked to the composition of also non-mercury methylating bacterial communities, likely providing growth substrate (e.g. acetate) for the hgcA-carrying microorganisms responsible for the actual methylation process. While previous research focused on mercury methylating microbial communities of wetlands, this study provides some first insights into the diversity of mercury methylating microorganisms in boreal forest soils.
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| 50. |
- Jingying, Xu, 1984-, et al.
(författare)
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Mercury Methylating Microbial Community Structure in Boreal Wetlands Explained by Local Physicochemical Conditions
- 2021
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Ingår i: Frontiers in Environmental Science. - : Frontiers Media S.A.. - 2296-665X. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- The potent neurotoxin methylmercury (MeHg) is a major concern due to its negative effects on wildlife and human health. Boreal wetlands play a crucial role in Hg cycling on a global scale, and therefore, it is crucial to understand the biogeochemical processes involved in MeHg formation in this landscape element. By combining high-throughput hgcA amplicon sequencing with molecular barcoding, we reveal diverse clades of potential Hg-II methylators in a wide range of wetland soils. Among Bacteria, Desulfuromonadota (14% of total reads), Desulfurobacterota_A, and Desulfurobacterota (up to 6% of total reads), previously classified as Deltaproteobacteria, were important members of the hgcA+ microbial community in the studied wetlands. We also identified Actinobacteriota (9.4% of total reads), Bacteroidota (2% of total reads), and Firmicutes (1.2% of total reads) as members of the hgcA+ microbial community. Within Archaea, Methanosarcinales represented up to 2.5% of the total reads. However, up to half of the hgcA+ community could not be resolved beyond domain Bacteria. Our survey also shows that local physicochemical conditions, such as pH, nutrient concentrations, water content, and prevailing redox states, are important for shaping the hgcA+ microbial community structure across the four studied wetlands. Furthermore, we observed a significant correlation between Hg-II methylation rate constants and the structure of the hgcA+ microbial community. Our findings expand the current knowledge on the hgcA+ microbial community composition in wetlands and the physicochemical factors underpinning spatial heterogeneity in such communities.
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