| 1. |
- Ambatipudi, Radhika, 1982-
(författare)
-
High Frequency (MHz) Planar Transformers for Next Generation Switch Mode Power Supplies
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing the power density of power electronic converters while reducing or maintaining the same cost, offers a higher potential to meet the current trend inrelation to various power electronic applications. High power density converters can be achieved by increasing the switching frequency, due to which the bulkiest parts, such as transformer, inductors and the capacitor's size in the convertercircuit can be drastically reduced. In this regard, highly integrated planar magnetics are considered as an effective approach compared to the conventional wire wound transformers in modern switch mode power supplies (SMPS). However, as the operating frequency of the transformers increase from several hundred kHz to MHz, numerous problems arise such as skin and proximity effects due to the induced eddy currents in the windings, leakage inductance and unbalanced magnetic flux distribution. In addition to this, the core losses whichare functional dependent on frequency gets elevated as the operating frequency increases. Therefore, this thesis provides an insight towards the problems related to the high frequency magnetics and proposes a solution with regards to different aspects in relation to designing high power density, energy efficient transformers.The first part of the thesis concentrates on the investigation of high power density and highly energy efficient coreless printed circuit board (PCB) step-down transformers useful for stringent height DC-DC converter applications, where the core losses are being completely eliminated. These transformers also maintain the advantages offered by existing core based transformers such as, high coupling coefficient, sufficient input impedance, high energy efficiency and wide frequencyband width with the assistance of a resonant technique. In this regard, several coreless PCB step down transformers of different turn’s ratio for power transfer applications have been designed and evaluated. The designed multilayered coreless PCB transformers for telecom and PoE applications of 8,15 and 30W show that the volume reduction of approximately 40 - 90% is possible when compared to its existing core based counterparts while maintaining the energy efficiency of the transformers in the range of 90 - 97%. The estimation of EMI emissions from the designed transformers for the given power transfer application proves that the amount of radiated EMI from a multilayered transformer is lessthan that of the two layered transformer because of the decreased radius for thesame amount of inductance.The design guidelines for the multilayered coreless PCB step-down transformer for the given power transfer application has been proposed. The designed transformer of 10mm radius has been characterized up to the power level of 50Wand possesses a record power density of 107W/cm3 with a peak energy efficiency of 96%. In addition to this, the design guidelines of the signal transformer fordriving the high side MOSFET in double ended converter topologies have been proposed. The measured power consumption of the high side gate drive circuitvitogether with the designed signal transformer is 0.37W. Both these signal andpower transformers have been successfully implemented in a resonant converter topology in the switching frequency range of 2.4 – 2.75MHz for the maximum load power of 34.5W resulting in the peak energy efficiency of converter as 86.5%.This thesis also investigates the indirect effect of the dielectric laminate on the magnetic field intensity and current density distribution in the planar power transformers with the assistance of finite element analysis (FEA). The significanceof the high frequency dielectric laminate compared to FR-4 laminate in terms of energy efficiency of planar power transformers in MHz frequency region is also explored.The investigations were also conducted on different winding strategies such as conventional solid winding and the parallel winding strategies, which play an important role in the design and development of a high frequency transformer and suggested a better choice in the case of transformers operating in the MHz frequency region.In the second part of the thesis, a novel planar power transformer with hybrid core structure has been designed and evaluated in the MHz frequency region. The design guidelines of the energy efficient high frequency planar power transformerfor the given power transfer application have been proposed. The designed corebased planar transformer has been characterized up to the power level of 50W and possess a power density of 47W/cm3 with maximum energy efficiency of 97%. This transformer has been evaluated successfully in the resonant converter topology within the switching frequency range of 3 – 4.5MHz. The peak energy efficiency ofthe converter is reported to be 92% and the converter has been tested for the maximum power level of 45W, which is suitable for consumer applications such as laptop adapters. In addition to this, a record power density transformer has been designed with a custom made pot core and has been characterized in thefrequency range of 1 - 10MHz. The power density of this custom core transformer operating at 6.78MHz frequency is 67W/cm3 and with the peak energy efficiency of 98%.In conclusion, the research in this dissertation proposed a solution for obtaining high power density converters by designing the highly integrated, high frequency(1 - 10MHz) coreless and core based planar magnetics with energy efficiencies inthe range of 92 - 97%. This solution together with the latest semiconductor GaN/SiC switching devices provides an excellent choice to meet the requirements of the next generation ultra flat low profile switch mode power supplies (SMPS).
|
|
| 2. |
- Ghylin, Trevor W, et al.
(författare)
-
Comparative single-cell genomics reveals potential ecological niches for the freshwater acI Actinobacteria lineage
- 2014
-
Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 8:12, s. 2503-2516
-
Tidskriftsartikel (refereegranskat)abstract
- Members of the acI lineage of Actinobacteria are the most abundant microorganisms in most freshwater lakes; however, our understanding of the keys to their success and their role in carbon and nutrient cycling in freshwater systems has been hampered by the lack of pure cultures and genomes. We obtained draft genome assemblies from 11 single cells representing three acI tribes (acI-A1, acI-A7, acI-B1) from four temperate lakes in the United States and Europe. Comparative analysis of acI SAGs and other available freshwater bacterial genomes showed that acI has more gene content directed toward carbohydrate acquisition as compared to Polynucleobacter and LD12 Alphaproteobacteria, which seem to specialize more on carboxylic acids. The acI genomes contain actinorhodopsin as well as some genes involved in anaplerotic carbon fixation indicating the capacity to supplement their known heterotrophic lifestyle. Genome-level differences between the acI-A and acI-B clades suggest specialization at the clade level for carbon substrate acquisition. Overall, the acI genomes appear to be highly streamlined versions of Actinobacteria that include some genes allowing it to take advantage of sunlight and N-rich organic compounds such as polyamines, di- and oligopeptides, branched-chain amino acids and cyanophycin. This work significantly expands the known metabolic potential of the cosmopolitan freshwater acI lineage and its ecological and genetic traits.
|
|
| 3. |
- Krause, Sascha, et al.
(författare)
-
Trait-based approaches for understanding microbial biodiversity and ecosystem functioning
- 2014
-
Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 5, s. 251-
-
Forskningsöversikt (refereegranskat)abstract
- In ecology, biodiversity-ecosystem functioning (BEE) research has seen a shift in perspective from taxonomy to function in the last two decades, with successful application of trait-based approaches. This shift offers opportunities for a deeper mechanistic understanding of the role of biodiversity in maintaining multiple ecosystem processes and services. In this paper, we highlight studies that have focused on BEE of microbial communities with an emphasis on integrating trait-based approaches to microbial ecology. In doing so, we explore some of the inherent challenges and opportunities of understanding BEE using microbial systems. For example, microbial biologists characterize communities using gene phylogenies that are often unable to resolve functional traits. Additionally, experimental designs of existing microbial BEE studies are often inadequate to unravel BEE relationships. We argue that combining eco-physiological studies with contemporary molecular tools in a trait-based framework can reinforce our ability to link microbial diversity to ecosystem processes. We conclude that such trait-based approaches are a promising framework to increase the understanding of microbial BEE relationships and thus generating systematic principles in microbial ecology and more generally ecology.
|
|
| 4. |
|
|
| 5. |
- Lund, Anja, et al.
(författare)
-
Enhancement of beta phase crystals formation with the use of nanofillers in PVDF films and fibres
- 2011
-
Ingår i: Composites Science And Technology. - : Elsevier Ltd.. - 0266-3538 .- 1879-1050. ; 71:2, s. 222-229
-
Tidskriftsartikel (refereegranskat)abstract
- Nanoclay and carbon nanotubes (CNT) have been in focus recently as means of enhancing beta phase crystals formation in poly(vinylidene fluoride)(PVDF). Dominantly, the so-far work has been carried out on films/ thin sheets filled with nanoclay. It has been found, mainly from combined XRD and DSC data, that nanoclay influences the PVDF structure, and particularly the beta phase crystals formation is enhanced. Results published by various groups are in fairly good agreement. There are no results for nanoclay filled melt-spun PVDF fibres. The influence of CNT on PVDF structure has been less studied. XRD data indicating an enhancing role of multi-wall carbon nanotubes (MWNT) on beta phase crystals formation in solution compounded PVDF films are available. Published results for MWNT/PVDF films are not in good agreement. The only study into single-wall carbon nanotube (SWNT)/PVDF has been made on electrospun nanofibres. We explore above findings towards melt-spun nanofilled PVDF fibres. We present new results obtained by us for melt-spun PVDF fibres containing non-functionalized and amino-functionalized double-wall carbon nanotubes (DWNT). The key finding is that amino-DWNT can influence the beta to alpha polymorphic balance.
|
|
| 6. |
|
|
| 7. |
- Rychwalski, Rodney, 1945, et al.
(författare)
-
DWNT/PVDF melt-spun piezoelectric fibres
- 2011
-
Ingår i: NT11 International Conference on Science and Applications of Nanotubes, University of Cambridge, July 11-16, Cambridge (UK), 2011.
-
Konferensbidrag (refereegranskat)abstract
- Crystalline morphology in poly(vinylidene fluoride)(PVDF), in particular the presence of polar β phase crystals, is of utmost importance towards the material´s piezoelectricity. Nanoparticles have been in focus recently as means of enhancing β phase crystals formation in PVDF. Dominantly, the so-far work has been carried out on films/thin sheets. The influence of CNT on PVDF crystalline structure has been less investigated, however some results indicating an enhancing role of multi-wall carbon nanotubes (MWNT) in solution compounded PVDF films are available. Published results for MWNT/PVDF films are not in good agreement. The only study into single-wall carbon nanotube (SWNT)/PVDF has been made on electrospun nanofibres. An overview of results for PVDF films/sheets and fibres using various nanoparticles published and in the literature is given in [1]. In the present work we focus on melt-spun double-wall carbon nanotubes (DWNT)/PVDF fibres. We present new results for melt-spun PVDF fibres containing non-functionalized and amino-functionalized DWNT. The key finding is that amino-DWNT can favourably influence the β to α polymorphic balance. [1][1] A. Lund, C. Gustafsson, H. Bertilsson, R.W. Rychwalski, Compos. Sci. Tech., Vol. 71, 222-229 (2011)Acknowledgement: The Swedish Foundation for Strategic Research (SSF) is acknowledged (AL, RWR).
|
|
| 8. |
- Rychwalski, Rodney, 1945, et al.
(författare)
-
Towards piezoelectric nanocarbon/PVDF fibres
- 2011
-
Ingår i: A Nano Connect Scandinavia event NanoUpdate 2011, May 23-24, Helsingborg (Sweden), 2011.
-
Konferensbidrag (refereegranskat)
|
|
| 9. |
- Rystedt, Alma, et al.
(författare)
-
Effect of Botulinum Toxin Concentration on Reduction in Sweating : a randomized, double-blind study
- 2013
-
Ingår i: Acta Dermato-Venereologica. - : Medical Journals Sweden AB. - 0001-5555 .- 1651-2057. ; 93:6, s. 674-678
-
Tidskriftsartikel (refereegranskat)abstract
- Dose-response studies of botulinum toxin for reduction of sweating are sparse in the literature. The aim of this study was to determine the most appropriate concentrations of Botox (R), Dysport (R), Xeomin (R) and NeuroBloc (R), respectively, in order to achieve the greatest reduction in sweating, thus reducing the costs and increasing the safety of treatment. Four concentrations of each product were investigated. Intradermal injections of all products and concentrations were applied to the backs of 20 consenting subjects, in a randomized, double-blind manner. Areas of anhidrotic and hypohidrotic skin were measured with an iodine-starch test after 4, 8 and 12 weeks, respectively. Optimal concentrations were found to be 25 U/ml for Botox and Xeomin, approximately 100 U/ml for Dysport, and 50 U/ml for NeuroBloc. When comparing the mean anhidrotic area per unit for 100 U/ml of each product, the calculated dose conversion ratios were 1:1.6:1.2:1.3 (Botox:Dysport:Xeomin:NeuroBloc). If, instead, the optimal concentration for each product was compared, the dose conversion ratios were 1:4.8:1.3:2.2. Thus, it is crucial to consider botulinum toxin concentration in a treatment regimen.
|
|
