| 1. |
- Danielson, E., et al.
(författare)
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Investigation of thermal properties in fabricated 4H-SiC high power bipolar transistors
- 2003
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Ingår i: Solid-State Electronics. - 0038-1101 .- 1879-2405. ; 47:4, s. 639-644
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Tidskriftsartikel (refereegranskat)abstract
- Silicon carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximum current gain of approximately 10 times, and a breakdown voltage of 450 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 degreesC, using the assumption that the current gain only depends on temperature. Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increase in the vicinity of the device. The device was also tested in a switched setup, showing fast turn on and turn off at 1 MHz and 300 V supply voltage. Device simulations have been used to analyze the measured data. The thermal conductivity is fitted against the self-heating, and the lifetime in the base is fitted against the measurement of the current gain.
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| 2. |
- Danielsson, Erik, et al.
(författare)
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Investigation of thermal properties in fabricated 4H-SiC high-power bipolar transistors
- 2002
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 389-393:2, s. 1337-1340
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Tidskriftsartikel (refereegranskat)abstract
- Silicon Carbide bipolar junction transistors have been fabricated and investigated. The transistors had a maximmn current gain of approximately 10 times, and a breakdown voltage of up to 600 V. When operated at high power densities the device showed a clear self-heating effect, decreasing the current gain. The junction temperature was extracted during self-heating to approximately 150 °C, using the assumption that the current gain only depends on temperature. Thermal images of a device under operation were also recorded using an infrared camera, showing a significant temperature increase in the vicinity of the device. Physical device simulations have been used to analyze the measured data. The thermal conductivity is fitted to model the measured self-heating, and the lifetime in the base is fitted against the measurement of the current gain.
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| 3. |
- Forsberg, Håkan, 1981-, et al.
(författare)
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Education as Field and Market : The Case of Upper Secondary School in Stockholm, 2006–2008
- 2019
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Ingår i: Empirical Investigations of Social Space. - Cham : Springer Publishing Company. - 9783030153861 - 9783030153878 ; , s. 245-266
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Bokkapitel (refereegranskat)abstract
- In the last three decades, Swedish education has undergone profound transformations, including a gradually increasing degree of privatization and marketization. These transformations offer an opportunity to analyse the relation between social space, education as social field and an emerging educational market. A correspondence analysis (CA) of all pupils attending all upper secondary educations in the Stockholm area in 2006–2008, with Euclidean classification as an additional analytic instrument, reveals that the social structure of the field of upper secondary education remains largely the same in spite of the market-oriented reforms. The embodied form of the unequally distributed social and cultural assets of which this structure is an expression, habitus, is particularly important for explaining both the distance and the responsiveness to marketization which characterize and separate elite schools, from medium and lower-ranked schools. It is concluded that the “market” should be understood as embedded in a social field of education that, in turn, reflects the polarities of the larger social space.
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| 4. |
- Forsberg, Håkan, 1981-
(författare)
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Kampen om eleverna : Gymnasiefältet och skolmarknadens framväxt i Stockholm, 1987–2011
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Swedish educational reforms in the beginning of the 1990s, introducing a public-funded voucher system, free school choice and the right to run schools as commercial enterprises, had an important impact on upper secondary education. The Stockholm region, the most populous in Sweden, offered favourable conditions for the growth of a previously non-existent educational market. A massive expansion of independent schools took place, managed primarily by larger companies, along with the extensive marketing of profiled study programmes and the import of management models from the private sector. In 2011 alone, schools competed for 75 000 pupils representing an annual economic value of approximately 8.5 billion SEK.Covering the period 1988 to 2011, this thesis analyses the relationship between the educational market and upper secondary education as a social field structured by the educational strategies of social groups. Building on Bourdieu’s relational sociology, the study combines quantitative and qualitative methods, using correspondence analysis as a major analytical tool.While free school choice and the voucher system established a supply-demand relationship between schools and families and pupils, the analysis shows that the market has submitted to the same forces that structure the field of upper secondary education within which it unfolds, primarily the volume and composition of symbolic and other assets that students, families and schools possess. In fact, the social structure of the field of upper secondary education in Stockholm remains remarkably stable over time, opposing on the one hand female and male dominated education and on the other hand education with high social and scholarly recruitment to that with low. Euclidean clustering analysis unveils a complex social structure reflecting how the increasingly differentiated educational supply has adapted to the needs of various social groups. Elite schools, market-oriented schools and market-exposed schools develop different strategies in the battle over pupils. Competing amongst themselves for pupils rich in inherited and acquired capital, the elite schools withdraw from the openly market-oriented approach that characterises the other type of schools and instead opt for more subtle, long-term strategies for building up trust from their audience, involving investments in staff and other institutional assets.
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| 5. |
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| 6. |
- Forsberg, Kalle, et al.
(författare)
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A Systematic Review Of Erythropoietin In Experimental Stroke
- 2009
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Ingår i: Stroke. - 0039-2499. ; 40:4
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Konferensbidrag (refereegranskat)abstract
- Introduction: Erythropoietin (EPO), a hematopoietic growth factor, has promise as a neuroprotectant in animal models of ischemic stroke. EPO is thought not only to protect neurons from cell death, but also is hypothesized to promote regeneration post stroke. Here we report a systematic review and meta-analysis of the published animal data characterizing the efficacy of EPO. Methods We conducted a systematic review and random effects weighted mean difference meta-analysis only including studies describing the efficacy of EPO in models of focal cerebral ischemia. Primary outcomes were infarct size and neurobehavioral score. A stratified analysis to identify the impact of elements of study quality and design was also conducted. Results Only 11 of 943 studies met our inclusion criteria. Infarct size was reported in 15 experiments using 191 animals. Neurobehavioral score was reported in 16 experiments using 287 animals. EPO improved infarct size by 30.5% (95%Cl 19.3%-41.7%) and neurobehavioral score by 37.4% (31.2– 43.7%). For infarct size, EPO was least effective in thrombotic models of ischemia, (16% versus to 44.8% and 24% in permanent and transient models of ischemia respectively, X2 =1.47 x 10–04). Using a scoring system derived from the STAIR criteria,study quality was modest with a median score of 4 out of 11 for both outcomes. Studies that randomized to treatment group reported smaller infarct sizes compared to those that did not (18.0% versus 44.8%, n=113 versus 78 animals, X2 = 3.4 x 10–05). Studies that blinded assessment of outcome also showed a smaller improvement in neurobehavioral score (31.1% versus 41.6%, n=107 versus 167, X2 = 8.9 x 10–4). Only 11.7% of the animals in the total dataset had a co-morbidity common to human stroke (hypertension) and this co-morbidity was only reported for neurobehavioral comparisons, not for infarct size. Blinded induction of ischemia was reported in 2 experiments (21.5% of animals) measuring infarct volume. Conclusions: Aggregation of the animal data for EPO in ischemic stroke indicates mean effect sizes of 30.5% and 37.4% for infarct volume and neurobehavioral score respectively. However, when the impact of common sources of bias are considered these effect sizes fall suggesting we are overestimating its potential benefit. As common human co-morbidities may reduce therapeutic efficacy, broader testing to delineate the range of circumstances in which EPO works would be beneficial before clinical trialing.
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| 7. |
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| 8. |
- Forsberg, Pontus, et al.
(författare)
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Diamond grating waveplates
- 2016
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Ingår i: Optical Materials Express. - : Optical Society of America. - 2159-3930 .- 2159-3930. ; 6:6, s. 2024-2030
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Tidskriftsartikel (refereegranskat)abstract
- Two designs of diamond quarter-wave plates for CO2 lasers, based on the birefringence of sub-wavelength gratings, were manufactured and tested. In one design the grating was etched on the surface of a 300 mu m thick polycrystalline diamond substrate. The other consisted of a diamond grating hanging freely in air, suspended at the edges from a silicon frame. The free-hanging design, while more fragile, had several advantages both in terms of fabrication and performance such as a larger grating period, higher transmission, and no need for an antireflective treatment of the backside.
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| 9. |
- Koo, S. -M, et al.
(författare)
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Influence of trenching effect on the characteristics of buried-gate SiC junction field-effect transistors
- 2002
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 389-393:2, s. 1235-1238
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Tidskriftsartikel (refereegranskat)abstract
- Two different structures of junction field-effect transistors in 4H-SiC, with and without trenching effect in the channel region, have been fabricated and characterized. The devices formed with metal mask show a trenching profile (>∌0.2 Όm) after dry etch in the channel groove region and exhibited static induction transistor (SIT)-like characteristics in the sub-threshold region of I-V curves as the channel thickness decreases. The devices without trenching effect have been processed by using a wet-etched oxide mask resulting in a sloped dry-etch profile (Ξ=∌30°) in the channel, and consequently showed well-saturated drain characteristics for all the channel thicknesses. The conduction mechanisms in these JFETs are examined by the potential profiles from two dimensional numerical simulations.
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| 10. |
- Koo, S. -M, et al.
(författare)
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Simulation and Measurement of Switching Characteristics of 4H-SiC Buried-Gate JFETs
- 2003
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 433-436, s. 773-776
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Tidskriftsartikel (refereegranskat)abstract
- Buried-gate junction field-effect transistors (JFETs) have been fabricated in 4H polytype silicon carbide (SiC). The dynamic switching characteristics of the JFETs in a circuit with inductive load have been characterized. The drain voltage rise/fall time of ∌30 ns and 25 ns have been observed for turn-off and turn-on, respectively. The results have been compared to numerical mixed-mode circuit simulations with finite element structures.
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