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  • Disputas: 2018-12-18 10:15 Planck, Fysikhuset, Linköping
    Lilja, Louise
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Halvledarmaterial. Linköpings universitet, Tekniska fakulteten.
    4H-SiC epitaxy investigating carrier lifetime and substrate off-axis dependence2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Silicon carbide (SiC) is a wide bandgap semiconductor with unique material properties making it useful for various device applications using high power, high frequency and high temperature. Compared to Si-based electronics, SiC based electronics have an improved energy efficiency. One of the most critical problems is to reduce this planets power consumption, where large improvements can be made enhancing the energy efficiency. Independent on how the electrical power is generated, power conversion is needed and about 10% of the electrical power is lost for every power conversion step using Si-based electronics. Since the efficiency is related to the performance of the semiconductor device, SiC can make contributions to the efficiency. Compared to Si, SiC has three times larger bandgap, about ten times higher breakdown electric field strength and about three times higher thermal conductivity. The wide bandgap together with the chemical stability of SiC makes it possible for SiC electronic devices to operate at much higher temperatures (>250°C) compared to Si-based devices and do not require large cooling units as with Si power converters.

    The current status for 4H-SiC devices regard unipolar devices (≤ 1700 V), such as metal-oxide-semiconductor field-effect transistors (MOSFETs) and Schottky barrier diodes (SBDs), are now on the market for mass production. The research focus is now on high-voltage (>10 kV) bipolar devices, such as, bipolar junction transistors (BJTs), p‑i‑n diodes and insulated-gate bipolar transistors (IGBTs).

    The focus of this thesis are material improvements relevant for the development of 4H-SiC high-voltage bipolar devices. A key parameter for such devices is the minority carrier lifetime, where long carrier lifetimes reduce the on-resistance through conductivity modulation. However, too long carrier lifetimes give long reverse recovery times leading to large switching losses. Thus, a tailored carrier lifetime is needed for the specific application. Carrier lifetimes of the epilayers can both be controlled by the CVD growth conditions and by post-growth processing, such as thermal oxidation and carbon implantation followed by thermal annealing. Emphasis in this thesis (Paper 1‑2) is to find optimal CVD growth conditions (growth temperature, C/Si ratio, growth rate, doping) improving the carrier lifetime. Since the main lifetime limiting defect has shown to be the Z1/2 center, identified as isolated carbon vacancies, growth conditions minimizing the Z1/2 concentration are strived for.

    To achieve high-voltage bipolar devices, thick epilayers of high quality is needed. An important factor is then the growth rate that needs to be relatively high in order to reduce the fabrication time, and thus the cost of the final device. In this thesis the growth process has been optimized for high growth rates (30 µm/h) using standard silane and propane chemistry (Paper 3), compared to other chemistries that includes chlorine, which results in corroded reactor parts and new defects in the epitaxial layers.

    Another important parameter for 4H-SiC bipolar devices is the basal plane dislocations (BPDs) in the substrate and epilayers, since the BPDs can act as source of nucleation and expansion of Shockley stacking faults (SSFs). The expanded SSFs give a lowered carrier lifetime and form a potential barrier for carrier transport leading to an increased forward voltage drop which in turn leads to bipolar degradation. The bipolar degradation is detrimental for 4H-SiC bipolar devices. Several strategies are developed to reduce the density of BPDs including buffer layers, growth interrupts and decreasing the substrates off-cut angle. Paper 4‑6 is focused on developing a CVD growth process for low substrate off-cut angles (1° and 2°) compared to the today’s standard off-cut angle of 4°. By reducing the substrate off-cut angle the number of BPDs intersecting the substrate surface is reduced. In addition, the conversion from BPDs to threading edge dislocations (TEDs) during epitaxial growth is increased with lower off-cut angles.

    Delarbeid
    1. Influence of Growth Temperature on Carrier Lifetime in 4H-SiC Epilayers
    Åpne denne publikasjonen i ny fane eller vindu >>Influence of Growth Temperature on Carrier Lifetime in 4H-SiC Epilayers
    Vise andre…
    2013 (engelsk)Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    Carrier lifetime and formation of defects have been investigated as a function of growth temperature in n-type 4H-SiC epitaxial layers, grown by horizontal hot-wall CVD. Emphasis has been put on having fixed conditions except for the growth temperature, hence growth rate, doping and epilayer thickness were constant in all epilayers independent of growth temperature. An increasing growth temperature gave higher Z1/2 concentrations along with decreasing carrier lifetime. A correlation between growth temperature and D1 defect was also observed.

    sted, utgiver, år, opplag, sider
    Trans Tech Publications Inc., 2013
    Emneord
    Atomic Force Microscopy, Carrier Lifetime, DLTS, Epitaxial Growth, Horizontal Hot-Wall CVD, Intrinsic Defect, Photoluminescence (PL)
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-88341 (URN)10.4028/www.scientific.net/MSF.740-742.637 (DOI)000319785500151 ()
    Konferanse
    9th European Conference on Silicon Carbide and Related Materials (ECSCRM 2012), 2-6 September 2012, St Petersburg, Russia
    Tilgjengelig fra: 2013-02-04 Laget: 2013-02-04 Sist oppdatert: 2018-12-10
    2. Smooth 4H-SiC epilayers grown with high growth rates with silane/propane chemistry using 4° off-cut substrates
    Åpne denne publikasjonen i ny fane eller vindu >>Smooth 4H-SiC epilayers grown with high growth rates with silane/propane chemistry using 4° off-cut substrates
    2016 (engelsk)Inngår i: Silicon Carbide and Related Materials 2015 / [ed] Fabrizio Roccaforte, Francesco La Via, Roberta Nipoti, Danilo Crippa, Filippo Giannazzo and Mario Saggio, Trans Tech Publications, 2016, Vol. 858, s. 209-212Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    4H-SiC epilayers with very smooth surfaces were grown with high growth rates on 4° off-cut substrates using standard silane/propane chemistry. Specular surfaces with RMS values below 0.2 nm are presented for epilayers grown with growth rates up to 30 μm/h using horizontal hot-wall chemical vapor deposition, with up to 100 μm thickness. Optimization of in-situ etching conditions and C/Si ratio are presented.

    sted, utgiver, år, opplag, sider
    Trans Tech Publications, 2016
    Serie
    Materials Science Forum, ISSN 1662-9752 ; 858
    Emneord
    Atomic force microscopy, Chemical vapor deposition, Epitaxial growth, Silicon carbide
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-153288 (URN)10.4028/www.scientific.net/MSF.858.209 (DOI)
    Konferanse
    The 16th International Conference on Silicon Carbide and Related Materials (ICSCRM2015), Giardini Naxos, Sicily, Italy, October 4th October 9th, 2015.
    Tilgjengelig fra: 2018-12-10 Laget: 2018-12-10 Sist oppdatert: 2018-12-10
    3. Improved Epilayer Surface Morphology on 2 degrees off-cut 4H-SiC Substrates
    Åpne denne publikasjonen i ny fane eller vindu >>Improved Epilayer Surface Morphology on 2 degrees off-cut 4H-SiC Substrates
    2014 (engelsk)Inngår i: SILICON CARBIDE AND RELATED MATERIALS 2013, PTS 1 AND 2, Trans Tech Publications , 2014, Vol. 778-780, s. 206-209Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    Homoepitaxial layers of 4H-SiC were grown with horizontal hot-wall CVD on 2 degrees off-cut substrates, with the purpose of improving the surface morphology of the epilayers and reducing the density of surface morphological defects. In-situ etching conditions in either pure hydrogen or in a mixture of silane and hydrogen prior to the growth were compared as well as C/Si ratios in the range 0.8 to 1.0 during growth. The smoothest epilayer surface, together with lowest defect density, was achieved with growth at a C/Si ratio of 0.9 after an in-situ etching in pure hydrogen atmosphere.

    sted, utgiver, år, opplag, sider
    Trans Tech Publications, 2014
    Serie
    Materials Science Forum, ISSN 1662-9752 ; 778-780
    Emneord
    epitaxial growth; horizontal hot-wall CVD; atomic force microscopy; vicinal off angle
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-108194 (URN)10.4028/www.scientific.net/MSF.778-780.206 (DOI)000336634100048 ()
    Konferanse
    SILICON CARBIDE AND RELATED MATERIALS 2013
    Tilgjengelig fra: 2014-06-26 Laget: 2014-06-26 Sist oppdatert: 2018-12-10
    4. In-grown stacking-faults in 4H-SiC epilayers grown on 2 degrees off-cut substrates
    Åpne denne publikasjonen i ny fane eller vindu >>In-grown stacking-faults in 4H-SiC epilayers grown on 2 degrees off-cut substrates
    2015 (engelsk)Inngår i: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 252, nr 6, s. 1319-1324Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    4H-SiC epilayers were grown on 2 degrees off-cut substrates using standard silane/propane chemistry, with the aim of characterizing in-grown stacking faults. The stacking faults were analyzed with low temperature photoluminescence spectroscopy, room temperature photoluminescence mappings, room temperature cathodoluminescence and synchrotron white beam X-ray topography. At least three different types of in-grown stacking faults were observed, including double Shockley stacking faults, triple Shockley stacking faults and bar-shaped stacking faults. Those stacking faults are all previously found in 4 degrees and 8 degrees off-cut epilayers; however, the geometrical size is larger in epilayers grown on 2 degrees off-cut substrates due to lower off-cut angle. The stacking faults were formed close to the epilayer/substrate interface during the epitaxial growth. (C) 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim

    sted, utgiver, år, opplag, sider
    WILEY-V C H VERLAG GMBH, 2015
    Emneord
    chemical vapor deposition; epitaxy; photoluminescence; SiC; stacking faults
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-120065 (URN)10.1002/pssb.201451710 (DOI)000355756200018 ()
    Merknad

    Funding Agencies|Swedish Research Council (VR); Advanced Functional Materials (AFM); Swedish Foundation for Strategic Research (SSF)

    Tilgjengelig fra: 2015-07-06 Laget: 2015-07-06 Sist oppdatert: 2018-12-10
  • Disputas: 2018-12-19 09:15 Planck, Fysikhuset, Linköping
    Lundström, Maria
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Biologi. Linköpings universitet, Tekniska fakulteten.
    Exploring Fennoscandian agricultural history through genetic analysis of aged crop materials2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Crop plants have undergone a multitude of genetic changes during and following their domestication. The spread of agriculture brought the crops to new geographic regions exposing them to new environments and selection pressures along the way. This gave rise to many local variants with traits favoured both by agricultural practices and the environment.

    Agriculture was introduced in Fennoscandia (Norway, Sweden, Finland and Denmark) around 4000 BC. The composition of the archaeobotanical record gives some clues as to which species were cultivated, but macroscale analyses rarely reach beyond that. Therefore, methods like genetic analysis are necessary to expand our knowledge about the history of crop cultivation. Under optimal conditions, DNA can survive in biological samples for several hundred thousand years. The preservation of plant specimens in the Fennoscandian climate has, however, rarely been explored. This thesis therefore attempts to dive deeper into the Fennoscandian cultivation history through genetic analyses of aged plant materials from both museum collections and archaeological sources. Cereal grains from a range of preservation conditions were evaluated to find which ones might be of interest for genetic investigations. Desiccated materials gave the highest success rates, in agreement with previous studies. Waterlogged materials appeared to contain small amounts of endogenous DNA, whereas genetic analysis of charred cereals failed completely in all samples.

    Population structure was investigated in 17-19th century materials of both barley and rye from Sweden and Finland. Northern and southern populations of Finnish six-row barley were distinct from one another. In southern Sweden, genetic analysis suggested conserved population structure extending over 200 years. The genetic composition of rye also seemed mostly conserved, but rye did not show geographic population structure across the investigated region in Sweden and Finland.

    A long-standing question in Fennoscandian crop history has been the interpretation of historical written records mentioning Brassica (cole crops, turnips and mustards), as well as the species identity of archaeobotanical finds of Brassica seeds. Thus, Next Generation Sequencing (NGS) was applied to identify which Brassica types that were cultivated in 17th century Kalmar, Sweden. The analysis corroborated morphological species classification in two of the investigated subfossil seeds, whereas no conclusions could be drawn from the remaining samples. The genome coverages were too low to allow subspecies identification.

    Wheat has been cultivated in Fennoscandia since the introduction of agriculture but has increased dramatically in importance over the last century. The functional allele of the wheat nutrition gene NAM-B1 was found to be particularly prominent in Fennoscandian wheats, likely associated with its effect on grain maturation time. Here the evolutionary history of NAM-B1 was investigated to see if it could truly be considered a domestication gene as suggested in a previous study. By studying extant landrace materials of Mediterranean tetraploid wheat, it was found that the non-functional allele showed signs indicative of a selective sweep. This selection did not, however, appear to have occurred during domestication.

    In conclusion, aged plant specimens from both museum and archaeological contexts could contribute greatly to our knowledge about historical cultivation, extending the investigated period into the mid 17th century. Subfossil and waterlogged archaeobotanical materials do contain endogenous DNA, suggesting that they are better suited for genetic analysis than charred ones, at least as far as cereals are concerned. There is potential for classifying archaeological Brassica remains using NGS, even though further optimisation of sample and library preparation may be necessary. And finally, despite NAM-B1 showing signs of selection it should not be considered a domestication gene in tetraploid wheat.

    Delarbeid
    1. Genetic analyses of Scandinavian desiccated, charred and waterlogged remains of barley (Hordeum vulgare L.)
    Åpne denne publikasjonen i ny fane eller vindu >>Genetic analyses of Scandinavian desiccated, charred and waterlogged remains of barley (Hordeum vulgare L.)
    Vise andre…
    2018 (engelsk)Inngår i: Journal of Archaeological Science: Reports, ISSN 2352-409X, Vol. 22, s. 11-20Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Barley, Hordeum vulgare L., has been cultivated in Fennoscandia (Denmark, Norway, Sweden, Finland) since the start of the Neolithic around 4000 years BCE. Genetic studies of extant and 19th century barley landraces from the area have previously shown that distinct genetic groups exist with geographic structure according to latitude, suggesting strong local adaptation of cultivated crops. It is, however, not known what time depth these patterns reflect. Here we evaluate different archaeobotanical specimens of barley, extending several centuries in time, for their potential to answer this question by analysis of aDNA. Forty-six charred grains, nineteen waterlogged specimens and nine desiccated grains were evaluated by PCR and KASP genotyping. The charred samples did not contain any detectable endogenous DNA. Some waterlogged samples permitted amplification of endogenous DNA, however not sufficient for subsequent analysis. Desiccated plant materials provided the highest genotyping success rates of the materials analysed here in agreement with previous studies. Five desiccated grains from a grave from 1679 in southern Sweden were genotyped with 100 SNP markers and data compared to genotypes of 19th century landraces from Fennoscandia. The results showed that the genetic composition of barley grown in southern Sweden changed very little from late 17th to late 19th century and farmers stayed true to locally adapted crops in spite of societal and agricultural development.

    sted, utgiver, år, opplag, sider
    Elsevier, 2018
    Emneord
    Ancient DNA, Barley, Population structure, 17th century, Landraces
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-151282 (URN)10.1016/j.jasrep.2018.09.006 (DOI)
    Tilgjengelig fra: 2018-09-14 Laget: 2018-09-14 Sist oppdatert: 2018-12-11bibliografisk kontrollert
    2. Archaeological and Historical Materials as a Means to Explore Finnish Crop History
    Åpne denne publikasjonen i ny fane eller vindu >>Archaeological and Historical Materials as a Means to Explore Finnish Crop History
    Vise andre…
    2018 (engelsk)Inngår i: Environmental Archaeology, ISSN 1461-4103, E-ISSN 1749-6314Artikkel i tidsskrift (Fagfellevurdert) Epub ahead of print
    Abstract [en]

    In Northern Europe, barley (Hordeum vulgare L.) has been cultivated for almost 6000 years. Thus far, 150-year-old grains from historical collections have been used to investigate the distribution of barley diversity and how the species has spread across the region. Genetic studies of archaeobotanical material from agrarian sites could potentially clarify earlier migration patterns and cast further light on the origin of barley landraces. In this study, we aimed to evaluate different archaeological and historical materials with respect to DNA content, and to explore connections between Late Iron Age and medieval barley populations and historical samples of barley landraces in north-west Europe. The material analysed consisted of archaeological samples of charred barley grains from four sites in southern Finland, and historical material, with 33 samples obtained from two herbaria and the seed collections of the Swedish museum of cultural history.

    The DNA concentrations obtained from charred archaeological barley remains were too low for successful KASP genotyping confirming previously reported difficulties in obtaining aDNA from charred remains. Historical samples from herbaria and seed collection confirmed previously shown strong genetic differentiation between two-row and six-row barley. Six-row barley accessions from northern and southern Finland tended to cluster apart, while no geographical structuring was observed among two-row barley. Genotyping of functional markers revealed that the majority of barley cultivated in Finland in the late nineteenth and early twentieth century was late-flowering under increasing day-length, supporting previous findings from northern European barley.

    sted, utgiver, år, opplag, sider
    Routledge, 2018
    Emneord
    aDNA, archaeobotany, barley, genetic diversity, Hordeum vulgare, KASP, landraces
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-151277 (URN)10.1080/14614103.2018.1482598 (DOI)2-s2.0-85048366875 (Scopus ID)
    Tilgjengelig fra: 2018-09-14 Laget: 2018-09-14 Sist oppdatert: 2018-12-11bibliografisk kontrollert
    3. Evolutionary history of the NAM-B1 gene in wild and domesticated tetraploid wheat
    Åpne denne publikasjonen i ny fane eller vindu >>Evolutionary history of the NAM-B1 gene in wild and domesticated tetraploid wheat
    2017 (engelsk)Inngår i: BMC Genetics, ISSN 1471-2156, E-ISSN 1471-2156, Vol. 18, artikkel-id 118Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Background

    The NAM-B1 gene in wheat has for almost three decades been extensively studied and utilized in breeding programs because of its significant impact on grain protein and mineral content and pleiotropic effects on senescence rate and grain size. First detected in wild emmer wheat, the wild-type allele of the gene has been introgressed into durum and bread wheat. Later studies have, however, also found the presence of the wild-type allele in some domesticated subspecies. In this study we trace the evolutionary history of the NAM-B1 in tetraploid wheat species and evaluate it as a putative domestication gene.

    Results

    Genotyping of wild and landrace tetraploid accessions showed presence of only null alleles in durum. Domesticated emmer wheats contained both null alleles and the wild-type allele while wild emmers, with one exception, only carried the wild-type allele. One of the null alleles consists of a deletion that covers several 100 kb. The other null-allele, a one-basepair frame-shift insertion, likely arose among wild emmer. This allele was the target of a selective sweep, extending over several 100 kb.

    Conclusions

    The NAM-B1 gene fulfils some criteria for being a domestication gene by encoding a trait of domestication relevance (seed size) and is here shown to have been under positive selection. The presence of both wild-type and null alleles in domesticated emmer does, however, suggest the gene to be a diversification gene in this species. Further studies of genotype-environment interactions are needed to find out under what conditions selection on different NAM-B1 alleles have been beneficial.

    sted, utgiver, år, opplag, sider
    BioMed Central, 2017
    Emneord
    Selective sweep, Grain protein content (GPC), Emmer, Durum, Domestication gene
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-144103 (URN)10.1186/s12863-017-0566-7 (DOI)000418687000001 ()
    Tilgjengelig fra: 2018-01-05 Laget: 2018-01-05 Sist oppdatert: 2018-12-11bibliografisk kontrollert
  • Disputas: 2018-12-19 13:15 Nobel BL32, B-Huset, Linköping
    Maghazeh, Arian
    Linköpings universitet, Institutionen för datavetenskap, Programvara och system. Linköpings universitet, Tekniska fakulteten.
    System-Level Design of GPU-Based Embedded Systems2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Modern embedded systems deploy several hardware accelerators, in a heterogeneous manner, to deliver high-performance computing. Among such devices, graphics processing units (GPUs) have earned a prominent position by virtue of their immense computing power. However, a system design that relies on sheer throughput of GPUs is often incapable of satisfying the strict power- and time-related constraints faced by the embedded systems.

    This thesis presents several system-level software techniques to optimize the design of GPU-based embedded systems under various graphics and non-graphics applications. As compared to the conventional application-level optimizations, the system-wide view of our proposed techniques brings about several advantages: First, it allows for fully incorporating the limitations and requirements of the various system parts in the design process. Second, it can unveil optimization opportunities through exposing the information flow between the processing components. Third, the techniques are generally applicable to a wide range of applications with similar characteristics. In addition, multiple system-level techniques can be combined together or with application-level techniques to further improve the performance.

    We begin by studying some of the unique attributes of GPU-based embedded systems and discussing several factors that distinguish the design of these systems from that of the conventional high-end GPU-based systems. We then proceed to develop two techniques that address an important challenge in the design of GPU-based embedded systems from different perspectives. The challenge arises from the fact that GPUs require a large amount of workload to be present at runtime in order to deliver a high throughput. However, for some embedded applications, collecting large batches of input data requires an unacceptable waiting time, prompting a trade-off between throughput and latency. We also develop an optimization technique for GPU-based applications to address the memory bottleneck issue by utilizing the GPU L2 cache to shorten data access time. Moreover, in the area of graphics applications, and in particular with a focus on mobile games, we propose a power management scheme to reduce the GPU power consumption by dynamically adjusting the display resolution, while considering the user's visual perception at various resolutions. We also discuss the collective impact of the proposed techniques in tackling the design challenges of emerging complex systems.

    The proposed techniques are assessed by real-life experimentations on GPU-based hardware platforms, which demonstrate the superior performance of our approaches as compared to the state-of-the-art techniques.

    Delarbeid
    1. General Purpose Computing on Low-Power Embedded GPUs: Has It Come of Age?
    Åpne denne publikasjonen i ny fane eller vindu >>General Purpose Computing on Low-Power Embedded GPUs: Has It Come of Age?
    2013 (engelsk)Inngår i: 13th International Conference on Embedded Computer Systems: Architectures, Modeling, and Simulation (SAMOS 2013), Samos, Greece, July 15-18, 2013., IEEE Press, 2013Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    In this paper we evaluate the promise held by low power GPUs for non-graphic workloads that arise in embedded systems. Towards this, we map and implement 5 benchmarks, that find utility in very different application domains, to an embedded GPU. Our results show that apart from accelerated performance, embedded GPUs are promising also because of their energy efficiency which is an important design goal for battery-driven mobile devices. We show that adopting the same optimization strategies as those used for programming high-end GPUs might lead to worse performance on embedded GPUs. This is due to restricted features of embedded GPUs, such as, limited or no user-defined memory, small instruction-set, limited number of registers, among others. We propose techniques to overcome such challenges, e.g., by distributing the workload between GPUs and multi-core CPUs, similar to the spirit of heterogeneous computation.

    sted, utgiver, år, opplag, sider
    IEEE Press, 2013
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-92626 (URN)10.1109/SAMOS.2013.6621099 (DOI)000332458100004 ()
    Konferanse
    SAMOS'13
    Tilgjengelig fra: 2013-05-14 Laget: 2013-05-14 Sist oppdatert: 2018-12-07
    2. Saving Energy without Defying Deadlines on Mobile GPU-based Heterogeneous Systems
    Åpne denne publikasjonen i ny fane eller vindu >>Saving Energy without Defying Deadlines on Mobile GPU-based Heterogeneous Systems
    Vise andre…
    2014 (engelsk)Inngår i: 2014 International Conference on Hardware/Software Codesign and System Synthesis, Association for Computing Machinery (ACM), 2014Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    With the advent of low-power programmable compute cores based on GPUs, GPU-equipped heterogeneous platforms are becoming common in a wide spectrum of industries including safety-critical domains like the automotive industry. While the suitability of GPUs for throughput oriented applications is well-accepted, their applicability for real-time applications remains an open issue. Moreover, in mobile/embedded systems, energy-efficient computing is a major concern and yet, there has been no systematic study on the energy savings that GPUs may potentially provide. In this paper, we propose an approach to utilize both the GPU and the CPU in a heterogeneous fashion to meet the deadlines of a real-time application while ensuring that we maximize the energy savings. We note that GPUs are inherently built to maximize the throughput and this poses a major challenge when deadlines must be satisfied. The problem becomes more acute when we consider the fact that GPUs are more energy efficient than CPUs and thus, a naive approach that is based on maximizing GPU utilization might easily lead to infeasible solutions from a deadline perspective.

    sted, utgiver, år, opplag, sider
    Association for Computing Machinery (ACM), 2014
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-112689 (URN)10.1145/2656075.2656097 (DOI)978-1-4503-3051-0 (ISBN)
    Konferanse
    International Conference on Hardware/Software Codesign and System Synthesis (CODES+ISSS 2014), New Delhi, India, October 12-17, 2014
    Tilgjengelig fra: 2014-12-08 Laget: 2014-12-08 Sist oppdatert: 2018-12-07bibliografisk kontrollert
    3. Perception-aware power management for mobile games via dynamic resolution scaling
    Åpne denne publikasjonen i ny fane eller vindu >>Perception-aware power management for mobile games via dynamic resolution scaling
    Vise andre…
    2015 (engelsk)Inngår i: 2015 IEEE/ACM INTERNATIONAL CONFERENCE ON COMPUTER-AIDED DESIGN (ICCAD), IEEE , 2015, s. 613-620Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    Modern mobile devices provide ultra-high resolutions in their display panels. This imposes ever increasing workload on the GPU leading to high power consumption and shortened battery life. In this paper, we first show that resolution scaling leads to significant power savings. Second, we propose a perception-aware adaptive scheme that sets the resolution during game play. We exploit the fact that game players are often willing to trade quality for longer battery life. Our scheme uses decision theory, where the predicted user perception is combined with a novel asymmetric loss function that encodes users' alterations in their willingness to save power.

    sted, utgiver, år, opplag, sider
    IEEE, 2015
    Serie
    ICCAD-IEEE ACM International Conference on Computer-Aided Design, ISSN 1933-7760
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-124543 (URN)10.1109/ICCAD.2015.7372626 (DOI)000368929600084 ()978-1-4673-8388-2 (ISBN)
    Konferanse
    Computer-Aided Design (ICCAD), 2015 IEEE/ACM International Conference on 2-6 Nov. 2015 Austin, TX
    Tilgjengelig fra: 2016-02-02 Laget: 2016-02-02 Sist oppdatert: 2018-12-07
    4. Latency-Aware Packet Processing on CPU-GPU Heterogeneous Systems
    Åpne denne publikasjonen i ny fane eller vindu >>Latency-Aware Packet Processing on CPU-GPU Heterogeneous Systems
    Vise andre…
    2017 (engelsk)Inngår i: DAC '17 Proceedings of the 54th Annual Design Automation Conference 2017, New York, NY, USA: Association for Computing Machinery (ACM), 2017Konferansepaper, Publicerat paper (Fagfellevurdert)
    Abstract [en]

    In response to the tremendous growth of the Internet, towards what we call the Internet of Things (IoT), there is a need to move from costly, high-time-to-market specific-purpose hardware to flexible, low-time-to-market general-purpose devices for packet processing. Among several such devices, GPUs have attracted attention in the past, mainly because the high computing demand of packet processing applications can, potentially, be satisfied by these throughput-oriented machines. However, another important aspect of such applications is the packet latency which, if not handled carefully, will overshadow the throughput benefits. Unfortunately, until now, this aspect has been mostly ignored. To address this issue, we propose a method that considers the variable bit rate of the traffic and, depending on the current rate, minimizes the latency, while meeting the rate demand. We propose a persistent kernel based software architecture to overcome the challenges inherent in GPU implementation like kernel invocation overhead, CPU-GPU communication and memory access overhead. We have chosen packet classification as the packet processing application to demonstrate our technique. Using the proposed approach, we are able to reduce the packet latency on average by a factor of 3.5, compared to the state-of-the-art solutions, without any packet drop.

    sted, utgiver, år, opplag, sider
    New York, NY, USA: Association for Computing Machinery (ACM), 2017
    Serie
    Design Automation Conference DAC, ISSN 0738-100X
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-141212 (URN)10.1145/3061639.3062269 (DOI)000424895400129 ()2-s2.0-85023612665 (Scopus ID)978-1-4503-4927-7 (ISBN)
    Konferanse
    54th ACM/EDAC/IEEE Design Automation Conference (DAC), Austin, TX, USA, June 18-22, 2017
    Tilgjengelig fra: 2017-09-27 Laget: 2017-09-27 Sist oppdatert: 2018-12-07bibliografisk kontrollert
  • Disputas: 2019-01-11 13:00 ACAS, A Building, Linköping
    Odar, Susanne
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Industriell ekonomi. Linköpings universitet, Tekniska fakulteten.
    Managementinitiativ, mening och verksamhetsresultat: En retrospektiv studie av en teknikintensiv verksamhet2019Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [sv]

    I denna studie betraktas en organisations utveckling med ett meningsskapande-perspektiv, vilket kort innebär att handlingar skapar mening och mening skapar handlingar. Weicks (1995) inflytelserika tankemodell av meningsskapande har utvecklats till en modell och metod som kan tillämpas på ett empiriskt material. Utvecklingen inom ASEA/ABB reläverksamheten under en trettioårsperiod från tidigt 1980-tal till år 2010 beskrivs och analyseras.

    Studien handlar om att förstå hur organisationer utvecklas, och hur chefer och medarbetare kan påverka en organisations utveckling och bidra till verksamhetsresultat. Syftet har avgränsats genom valet av teoretiskt perspektiv, metod och forskningsfrågor. Forskningsfrågorna rör samspelet mellan så kallade managementinitiativ, mening och verksamhetens utveckling. Managementinitiativ är en typ av handlingar som chefer i en organisation kan besluta om. Hur dessa påverkar och påverkas av de uppfattningar som finns hos chefer och medarbetare i organisationen beskrivs och analyseras. Det valda fallet omfattar 85 stycken initiativ. Studien har visat att en verksamhets utveckling bäst förstås genom en analys av den aktuella verksamheten och dess omvärld, och att det går att finna mönster som upprepas över tid inom ramen för verksamheten

    Metoden och modellen är generaliserbara och kan användas för empiriska studier av meningsskapande i grupper, organisationer och samhällen. Det kanske viktigaste bidraget med modellen och metoden är att samspelet mellan olika nivåer – individ-, interaktions-, struktur- och kulturnivån – kan studeras över tid samt att fokus kan riktas mot substansen, innehållet, i meningsskapandet såväl som processen. Data omfattar handlingar, argument, förväntningar och utfästelser. I denna studie har dessa betraktats som uttryck för meningsskapande, men de kan ses som uttryck för andra perspektiv. Metoden och modellen kan även användas inom andra processtudier där dessa kategoriers utveckling över tiden är av intresse, och där samspelet mellan olika nivåer är av betydelse.

    Ambitionen är i första hand att bidra till det pågående samtalet inom meningsskapande, men en förhoppning är också göra området tillgängligt för forskare inom andra områden och praktiker som inte kommit i kontakt med meningsskapande tidigare.

  • Disputas: 2019-01-18 13:15 K3, Kåkenhus, Norrköping
    Dahlberg, Joen
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten.
    Cost allocation methods in cooperative transportation planning2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Transportation, together with transportation planning for goods, provides good conditions for economic growth and is a natural part of modern society. However, transportation has negative side effects, including emissions and traffic congestion. A freight forwarder may consolidate shippers’ goods in order to reduce some of the negative side effects, thus reducing emissions and/or congestion as well as operational costs. The negative side effects as well as operational costs can be further reduced if a number of freight forwarders cooperate and consolidate their collective goods flows. Consolidation refers to the process of merging a number of the freight forwarders’ shipments of goods into a single shipment. In this case, the freight forwarders are cooperating with competitors (the other freight forwarders).

    Fair cost allocations are important for establishing and maintaining cost-efficient cooperation among competing stakeholders. Cooperative game theory defines a number of criteria for fair cost allocations and the problem associated with the decision process for allocating costs is referred to as the cost allocation problem. In this thesis, cooperative game theory is used as an academic tool to study cooperation among stakeholders in two transportation planning applications, namely 1) the distribution of goods bound for urban areas and 2) the transportation of wood between harvest areas and industries.

    In transportation planning application 1, there is a cooperation among a number of freight forwarders and a municipality. Freight forwarders’ goods bound for an urban area are consolidated at a facility located just outside the urban area. In this thesis, operational costs for distributing the goods are assessed by solving vehicle routing problems. Common methods from cooperative game theory are used for allocating the operational costs among the freight forwarders and the municipality. In transportation planning application 2, forest companies cooperate in terms of the supply and transportation of common resources, or more specifically, different types of wood. Each forest company has harvest areas and industries to which the wood is transported. The resources may be bartered, that is, the forest companies may transport wood from each other’s harvest areas.

    In the cooperative game theory literature, the stakeholders are often treated equally in the context of transportation planning. However, there seems to be a lack of studies on cooperations where at least one stakeholder differs from the other stakeholders in some fundamental way, for instance, as an initiator or an enabler of the cooperation. Such cooperations are considered in this thesis. The municipality and one of the forest companies are considered to be the initiators in their respective applications.

    Five papers are appended to this thesis and the overall aim is to contribute to the research into cooperative transportation planning by using concepts from cooperative game theory to develop methods for allocating costs among cooperating stakeholders. The purpose of this thesis is to provide decision support for planners in the decisionmaking process of transportation planning to establish cost-efficient and stable cooperations.

    Some of the main outcomes of this thesis are viable and practical methods that could be used in real-life situations to allocate costs among cooperating stakeholders, as well as support for decisionmakers who are concerned with transportation planning. This is done by demonstrating the potential of cooperation, such as cost reduction, and by suggesting how costs can be allocated fairly in the transportation planning applications considered. Lastly, a contribution to cooperative game theory is provided; the introduction of a development of the equal profit method for allocating costs. The proposed version is the equal profit method with lexicography, which, in contrast to the former, guarantees to yield at most one solution to any cost allocation problem. Lexicography is used to rank potential cost allocations and the unambiguously best cost allocation is chosen.  

    Delarbeid
    1. Consolidation in Urban Freight Transportation - Cost Allocation Models
    Åpne denne publikasjonen i ny fane eller vindu >>Consolidation in Urban Freight Transportation - Cost Allocation Models
    2018 (engelsk)Inngår i: Asia-Pacific journal of operational research, ISSN 0217-5959, E-ISSN 1793-7019, Vol. 35, nr 4, artikkel-id 1850023Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    In this paper, the focus is on the role of the municipality, as an enabler of a collaboration between freight forwarders and the municipality in which the consolidation of goods is considered as a means for goods flow improvement in urban freight transportation. We present a cost allocation model that is based on solution concepts from cooperative game theory, for allocating the operational costs associated with the collaboration. It is assumed that the municipality is willing to carry some cost to ensure a stable collaboration for the potential benefits received, e.g., reduced traffic congestion in the city. The model is applied to some illustrative examples, and the cost allocation results are discussed. It is shown that the role of the municipality may be decisive in achieving a stable collaboration between the freight forwarders, and further that the municipality does not necessarily need to contribute to covering the costs.

    sted, utgiver, år, opplag, sider
    WORLD SCIENTIFIC PUBL CO PTE LTD, 2018
    Emneord
    Collaboration; cost allocation; city distribution center; municipality
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-150486 (URN)10.1142/S0217595918500239 (DOI)000441395200005 ()
    Merknad

    Funding Agencies|Swedish Energy Agency; VINNOVA

    Tilgjengelig fra: 2018-08-24 Laget: 2018-08-24 Sist oppdatert: 2018-12-13
    2. A note on the nonuniqueness of the Equal Profit Method
    Åpne denne publikasjonen i ny fane eller vindu >>A note on the nonuniqueness of the Equal Profit Method
    2017 (engelsk)Inngår i: Applied Mathematics and Computation, ISSN 0096-3003, E-ISSN 1873-5649, Vol. 308, s. 84-89Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    When a set of players cooperate, they need to decide how the collective cost should be allocated amongst them. Cooperative game theory provides several methods or solution concepts, that can be used as a tool for cost allocation. In this note, we consider a specific solution concept called the Equal Profit Method (EPM). In some cases, a solution to the EPM is any one of infinitely many solutions. That is, it is not always unique. This leads to a lack of clarity in the characterization of the solutions obtained by the EPM. We present a modified version of the EPM, which unlike its precursor ensures a unique solution. In order to illustrate the differences, we present some numerical examples and comparisons between the two concepts.

    Emneord
    Game Theory, Unique Solution, Solution Concept, EPM, Linear Programming, Lexicography
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121557 (URN)10.1016/j.amc.2017.03.018 (DOI)000399591500007 ()
    Merknad

    Funding agencies: Swedish Energy Agency

    Tilgjengelig fra: 2015-09-24 Laget: 2015-09-24 Sist oppdatert: 2018-12-13
    3. Incitements for transportation collaboration by cost allocation
    Åpne denne publikasjonen i ny fane eller vindu >>Incitements for transportation collaboration by cost allocation
    Vise andre…
    2018 (engelsk)Inngår i: Central European Journal of Operations Research, ISSN 1435-246X, E-ISSN 1613-9178Artikkel i tidsskrift (Fagfellevurdert) Epub ahead of print
    Abstract [en]

    In this paper, we focus on how cost allocation can be used as a means to create incentives for collaboration among companies, with the aim of reducing the total transportation cost. The collaboration is assumed to be preceded by a simultaneous invitation of the companies to collaborate. We make use of concepts from cooperative game theory, including the Shapley value, the Nucleolus and the EPM, and develop specific cost allocation mechanisms aiming to achieve large collaborations among many companies. The cost allocation mechanisms are tested on a case study that involves transportation planning activities. Although the case study is from a specific transportation sector, the findings in this paper can be adapted to collaborations in other types of transportation planning activities. Two of the cost allocation mechanisms ensure that any sequence of companies joining the collaboration represents a complete monotonic path, that is, any sequence of collaborating companies is such that the sequences of allocated costs are non-increasing for all companies.

    sted, utgiver, år, opplag, sider
    Springer, 2018
    Emneord
    Collaboration, Transportation planning, Monotonic Path, Cost Allocation, Cooperative game theory
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121558 (URN)10.1007/s10100-018-0530-2 (DOI)
    Forskningsfinansiär
    Swedish Energy AgencyVINNOVA
    Tilgjengelig fra: 2015-09-24 Laget: 2015-09-24 Sist oppdatert: 2018-12-13bibliografisk kontrollert
  • Disputas: 2019-01-23 10:15 BL32, B-huset, Linköping
    Shuaib, Budor
    Linköpings universitet, Matematiska institutionen, Matematik och tillämpad matematik. Linköpings universitet, Tekniska fakulteten.
    Ghostpeakons2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this thesis we study peakons (peaked solitons), a class of solutions which occur in certain wave equations, such as the Camassa–Holm shallow water equation and its mathematical relatives, the Degasperis–Procesi, Novikov and Geng– Xue equations. These four non-linear partial differential equations are all integrable systems in the sense of having Lax pairs, infinitely many conservation laws, and multipeakon solutions given by explicitly known formulas.

    In the first paper, we develop a method which uses so-called ghostpeakons (peakons with amplitude zero) to find explicit formulas for the characteristic curves associated with the multipeakon solutions of the Camassa–Holm, Degasperis– Procesi and Novikov equations.

    In the second paper, we use the ghostpeakon method to derive explicit formulas for arbitrary multipeakon solutions of the two-componentGeng–Xue equation. The general case involves many inequivalent peakons configurations, depending on the order in which the peakons occur in the two components of the solution, and previously the solution was known only in the so-called interlacing case where the peakons lie alternatingly in one component and in the other. To obtain the solution formulas for an arbitrary configuration, we introduce auxiliary peakons to make the configuration interlacing. By taking suitable limits, we then drive the amplitudes of the auxiliary peakons to zero, leaving the solution formulas for the remaining ordinary peakons. 

  • Disputas: 2019-01-25 13:00 ACAS, A-Building, Linköping
    Radits, Markus
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Industriell ekonomi. Linköpings universitet, Tekniska fakulteten.
    A Business Ecology Perspective on Community-Driven Open Source: The Case of the Free and Open Source Content Management System Joomla2019Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    This thesis approaches the phenomenon of open source software (OSS) from a managerial and organisational point of view. In a slightly narrower sense, this thesis studies commercialisation aspects around community-driven open source. The term ‘community-driven’ signifies open source projects that are managed, steered, and controlled by communities of volunteers, as opposed to those that are managed, steered, and controlled by single corporate sponsors.

    By adopting a business ecology perspective, this thesis places emphasis on the larger context within which the commercialisation of OSS is embedded (e.g., global and collaborative production regimes, ideological foundations, market characteristics, and diffuse boundary conditions). Because many business benefits arise as a consequence of the activities taking place in the communities and ecosystems around open source projects, a business ecology perspective may be a useful analytical guide for understanding the opportunities, challenges, and risks that firms face in commercializing OSS.

    There are two overarching themes guiding this thesis. The first theme concerns the challenges that firms face in commercialising community-driven open source. There is a tendency in the literature on business ecosystems and open source to emphasise the benefits, opportunities, and positive aspects of behaviour, at the expense of the challenges that firms face. However, business ecosystems are not only spaces of opportunity, they may also pose a variety of challenges that firms need to overcome in order to be successful. To help rectify this imbalance in the literature, the first theme particularly focuses on the challenges that firms face in commercialising community-driven open source. The underlying ambition is to facilitate a more balanced and holistic understanding of the collaborative and competitive dynamics in ecosystems around open source projects.

    The other theme concerns the complex intertwining of community engagement and profit-oriented venturing. As is acknowledged in the literature, the subject of firm-community interaction has become increasingly important because the survival, success, and sustainability of peer production communities has become of strategic relevance to many organisations. However, while many strategic benefits may arise as a consequence of firm-community interaction, there is a lack of research studying how the value-creating logics of firm–community interaction are embedded within the bigger picture in which they occur. Bearing this bigger picture in mind, this thesis explores the intertwining of volunteer community engagement and profit-oriented venturing by focusing on four aspects that are theorised in the literature: reinforcement, complementarity, synergy, and reciprocity.

    This thesis is designed as a qualitative exploratory single-case study. The empirical case is Joomla, a popular open source content management system. In a nutshell, the Joomla case in this thesis comprises the interactions in the Joomla community and the commercial activities around the Joomla platform (e.g., web development, consulting, marketing, customisation, extensions). In order to achieve greater analytical depth, the business ecology perspective is complemented with ideas and propositions from other theoretical areas, such as stakeholder theory, community governance, organizational identity, motivation theory, pricing, and bundling.

    The findings show that the common challenges in commercialising community-driven open source revolve around nine distinct factors that roughly cluster into three domains: the ecosystem, the community, and the firm. In short, the domain of the ecosystem comprises the global operating environment, the pace of change, and the cannibalisation of ideas. The domain of the community comprises the platform policy, platform image, and the voluntary nature of the open source project. And finally, the domain of the firm comprises the blurring boundaries between private and professional lives, the difficulty of estimating costs, and firm dependencies. Based on these insights, a framework for analysing community-based value creation in business ecosystems is proposed. This framework integrates collective innovation, community engagement, and value capture into a unified model of value creation in contexts of firm–community interaction.

    Furthermore, the findings reveal demonstrable effects of reinforcement, complementarity, synergy, and reciprocity in the intertwining of volunteer community engagement and profit-oriented venturing. By showing that this intertwining can be strong in empirical cases where commercial activities are often implicitly assumed to be absent, this thesis provides a more nuanced understanding of firm involvement in the realm of open source.

    Based on the empirical and analytical insights, a number of further theoretical implications are discussed, such as the role of intersubjective trust in relation to the uncertainties that commercial actors face, an alternative way of classifying community types, the metaphor of superorganisms in the context of open source, issues pertaining to the well-being of community participants, and issues in relation to the transitioning of open source developers from a community-based to an entrepreneurial self-identity when commercialising an open source solution. Furthermore, this thesis builds on six sub-studies that make individual contributions of their own.

    In a broad sense, this thesis contributes to the literature streams on the commercialisation of OSS, the business value and strategic aspects of open source, the interrelationships between community forms of organising and entrepreneurial activities, and the nascent research on ecology perspectives on peer-production communities. A variety of opportunities for future research are highlighted.