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Tolstoy G.,KTH Royal Institute of Technology | Peftitsis D.,KTH Royal Institute of Technology | Rabkowski J.,KTHRoyal Institute of Technology | Rabkowski J.,Warsaw University of Technology | And 2 more authors.
IEEE Transactions on Power Electronics | Year: 2014

Silicon carbide (SiC) bipolar junction transistors (BJTs) require a continuous base current in the on-state. This base current is usually made constant and is corresponding to the maximum collector current and maximum junction temperature that is foreseen in a certain application. In this paper, a discretized proportional base driver is proposed which will reduce, for the right application, the steady-state power consumption of the base driver. The operation of the proposed base driver has been verified experimentally, driving a 1200-V/40-A SiC BJT in a dc-dc boost converter. In order to determine the potential reduction of the power consumption of the base driver, a case with a dc-dc converter in an ideal electric vehicle driving the new European drive cycle has been investigated. It is found that the steady-state power consumption of the base driver can be reduced by approximately 60%. The total reduction of the driver consumption is 3459 J during the drive cycle, which is slightly more than the total on-state losses for the SiC BJTs used in the converter. © 2013 IEEE.


Eichhorn M.,French German Research Institute of Saint Louis | Pollnau M.,KTHRoyal Institute of Technology
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2014

We review the physics underlying the process of spontaneous emission, with a special focus on spontaneous emission into a resonator mode. We define the mode volume, verify the fundamental modal dimensions, present the spectral mode profile, the coherence time, the Q-factor, the Füchtbauer-Ladenburg equation, and the Purcell factor, and discuss their influence on different types of lasers. We obtain the relation between peak emission cross section, radiative lifetime, and emission linewidth. By interpreting spontaneous emission as stimulated emission driven by vacuum fluctuations, we derive the spontaneous-emission rate into a resonator mode and establish physical expressions for the fractions of spontaneous emission and total decay from the upper laser level into this mode. Furthermore, we discuss coupling of the atomic system with the coherent field inside a lasing resonator mode, resulting in the formation of a Mollow triplet, and demonstrate that it leads to a reduction of the spontaneous-emission rate by a factor of 2. © 1995-2012 IEEE.


Onifade I.,KTHRoyal Institute of Technology | Balieu R.,KTHRoyal Institute of Technology | Birgisson B.,Aston University
Mechanics of Time-Dependent Materials | Year: 2016

This paper presents a new interpretation for the Superpave IDT strength test based on a viscoelastic-damage framework. The framework is based on continuum damage mechanics and the thermodynamics of irreversible processes with an anisotropic damage representation. The new approach introduces considerations for the viscoelastic effects and the damage accumulation that accompanies the fracture process in the interpretation of the Superpave IDT strength test for the identification of the Dissipated Creep Strain Energy (DCSE) limit from the test result. The viscoelastic model is implemented in a Finite Element Method (FEM) program for the simulation of the Superpave IDT strength test. The DCSE values obtained using the new approach is compared with the values obtained using the conventional approach to evaluate the validity of the assumptions made in the conventional interpretation of the test results. The result shows that the conventional approach over-estimates the DCSE value with increasing estimation error at higher deformation rates. © 2016 Springer Science+Business Media Dordrecht


Uddenberg D.,Swedish University of Agricultural Sciences | Reimegard J.,KTHRoyal Institute of Technology | Clapham D.,Swedish University of Agricultural Sciences | Almqvist C.,Forestry Research Institute of Sweden | And 3 more authors.
Plant Physiology | Year: 2013

Conifers normally go through a long juvenile period, for Norway spruce (Picea abies) around 20 to 25 years, before developing male and female cones. We have grown plants from inbred crosses of a naturally occurring spruce mutant (acrocona). One-fourth of the segregating acrocona plants initiate cones already in their second growth cycle, suggesting control by a single locus. The early cone-setting properties of the acrocona mutant were utilized to identify candidate genes involved in vegetative-toreproductive phase change in Norway spruce. Poly(A+) RNA samples from apical and basal shoots of cone-setting and noncone- setting plants were subjected to high-throughput sequencing (RNA-seq). We assembled and investigated 33,383 expressed putative protein-coding acrocona transcripts. Eight transcripts were differentially expressed between selected sample pairs. One of these (Acr42124_1) was significantly up-regulated in apical shoot samples from cone-setting acrocona plants, and the encoded protein belongs to the MADS box gene family of transcription factors. Using quantitative real-time polymerase chain reaction with independently derived plant material, we confirmed that the MADS box gene is up-regulated in both needles and buds of cone-inducing shoots when reproductive identity is determined. Our results constitute important steps for the development of a rapid cycling model system that can be used to study gene function in conifers. In addition, our data suggest the involvement of a MADS box transcription factor in the vegetative-to-reproductive phase change in Norway spruce.


Mrtensson J.,KTHRoyal Institute of Technology | Rojas C.R.,KTHRoyal Institute of Technology | Hjalmarsson H.,KTHRoyal Institute of Technology
Automatica | Year: 2011

It is well known that if we intend to use a minimum variance control strategy, which is designed based on a model obtained from an identification experiment, the best experiment which can be performed on the system to determine such a model (subject to output power constraints, or for some specific model structures) is to use the true minimum variance controller. This result has been derived under several circumstances, first using asymptotic (in model order) variance expressions but also more recently for ARMAX models of finite order. In this paper we re-approach this problem using a recently developed expression for the variance of parametric frequency function estimates. This allows a geometric analysis of the problem and the generalization of the aforementioned finite model order ARMAX results to general linear model structures. © 2011 Elsevier Ltd. All rights reserved.


Yildirim H.C.,Aalto University | Marquis G.,Aalto University | Marquis G.,KTHRoyal Institute of Technology
Analysis and Design of Marine Structures - Proceedings of the 5th International Conference on Marine Structures, MARSTRUCT 2015 | Year: 2015

In the past decade, High Frequency Mechanical Impact (HFMI) has significantly developed as a reliable, effective and user-friendly method for post-weld fatigue strength improvement technique for welded steel structures. The evaluation and features of developing guideline within the International Institute of Welding (IIW) for the design of structures improved using HFMI is briefly discussed. So far, the extra fatigue strength benefit for HFMI-treated high strength steels has been mostly shown for constant amplitude loading. This paper reports 68 available HFMI-improved welds subjected to overloads or pre-fatigue loads at various loading conditions prior to fatigue testing. These loading conditions are often seen for marine structures. © 2015 Taylor & Francis Group, London.


Rojas C.R.,KTHRoyal Institute of Technology | Barenthin M.,KTHRoyal Institute of Technology | Welsh J.S.,University of Newcastle | Hjalmarsson H.,KTHRoyal Institute of Technology
Automatica | Year: 2011

In this paper we investigate the cost of complexity, which is defined as the minimum amount of input power required to estimate the frequency response of a given linear time invariant system of order n with a prescribed degree of accuracy. In particular we require that the asymptotic (in the data length) variance is less or equal to γ over a prespecified frequency range [0, ωB]. The models considered here are Output Error models, with an emphasis on fixed denominator and Laguerre models. Several properties of the cost are derived. For instance, we present an expression which shows how the pole of the Laguerre model affects the cost. These results quantify how the cost of the system identification experiment depends on n and on the model structure. Also, they show the relation between the cost and the amount of information we would like to extract from the system (in terms of ωB and γ). For simplicity we assume that there is no undermodelling. © 2011 Elsevier Ltd. All rights reserved.


Esparza A.,Polytechnic University of Valencia | Aguero J.C.,University of Newcastle | Rojas C.R.,KTHRoyal Institute of Technology | Godoy B.I.,University of Newcastle
Automatica | Year: 2011

In this paper, we generalize existing fundamental limitations on the accuracy of the estimation of dynamic models. In addition, we study the large sample statistical behavior of different estimation-based controller design strategies. In particular, fundamental limitations on the closed-loop performance using a controller obtained by Virtual Reference Feedback Tuning (VRFT) are studied. We also extend our results to more general estimation-based control design strategies. We present numerical examples to show the application of our results. © 2011 Elsevier Ltd. All rights reserved.


Mller C.,University of Newcastle | Rojas C.R.,KTHRoyal Institute of Technology | Goodwin G.C.,University of Newcastle
Automatica | Year: 2012

In this paper a real-time method for generating signals of constrained amplitude and a given (arbitrary) spectrum is presented. This technique is based on the concatenation of sinusoidal signals of suitably chosen frequencies in order to obtain a signal with the desired sample autocovariance sequence as the number of samples tends to infinity. The effectiveness of the method is demonstrated theoretically and via simulations. © 2011 Elsevier Ltd. All rights reserved.


Ayoglu B.,KTHRoyal Institute of Technology | Haggmark A.,KTHRoyal Institute of Technology | Khademi M.,Karolinska Institutet | Olsson T.,Karolinska Institutet | And 3 more authors.
Molecular and Cellular Proteomics | Year: 2013

Profiling the autoantibody repertoire with large antigen collections is emerging as a powerful tool for the identification of biomarkers for autoimmune diseases. Here, a systematic and undirected approach was taken to screen for profiles of IgG in human plasma from 90 individuals with multiple sclerosis related diagnoses. Reactivity pattern of 11,520 protein fragments (representing ̃38% of all human protein encoding genes) were generated on planar protein microarrays built within the Human Protein Atlas. For more than 2,000 antigens IgG reactivity was observed, among which 64% were found only in single individuals. We used reactivity distributions among multiple sclerosis subgroups to select 384 antigens, which were then reevaluated on planar microarrays, corroborated with suspension bead arrays in a larger cohort (n = 376) and confirmed for specificity in inhibition assays. Among the heterogeneous pattern within and across multiple sclerosis subtypes, differences in recognition frequencies were found for 51 antigens, which were enriched for proteins of transcriptional regulation. In conclusion, using protein fragments and complementary high-throughput protein array platforms facilitated an alternative route to discovery and verification of potentially disease-associated autoimmunity signatures, that are now proposed as additional antigens for large-scale validation studies across multiple sclerosis biobanks. © 2013 by The American Society for Biochemistry and Molecular Biology, Inc.

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