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  • 51. Adell, M
    et al.
    Kanski, J
    Stanciu, V
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Fasta tillståndets fysik.
    Ilver, L
    Sadowski, J
    Svedlindh, P
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Fasta tillståndets fysik.
    Comment on “Mn interstitial diffusion in (Ga,Mn)As”2005Ingår i: Phys. Rev. Lett., Vol. 94, s. 139701-Artikel i tidskrift (Refereegranskat)
  • 52. Adell, M
    et al.
    Staniciu, V
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Fasta tillståndets fysik.
    Kanski, J
    Ilver, L
    Sadowski, J
    Domagala, J Z
    Svedlindh, P
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik. Fasta tillståndets fysik.
    Terki, F
    Hernandez, C
    Charar, S
    Post-growth annealing of (Ga,Mn)As under As capping – an alternative way to increase Tc2005Ingår i: Apåpl. Phys. Lett., Vol. 86, s. 112501-Artikel i tidskrift (Refereegranskat)
  • 53. Adell, Martin
    et al.
    Ilver, Lars
    Kanski, Janusz
    Stanciu, Victor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Svedlindh, Peter
    Sadowski, Janusz
    Domagala, J.Z.
    Terki, F.
    Hernandez, C.
    Charar, S.
    Postgrowth annealing of (Ga,Mn)As under As capping: An alternative way to increase Tc2005Ingår i: Applied Physics Letters, Vol. 86, s. 112501-Artikel i tidskrift (Refereegranskat)
  • 54.
    Adolfsson, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Simplified finite element bearing modeling: with NX Nastran2015Självständigt arbete på grundnivå (yrkesexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This report was produced at the request of ABB Robotics and the work was conducted at their facilities in Västerås, Sweden.

    In the development of industrial robots the structures are slimmed to increase the accuracy and speed. When conducting finite element analysis on the robots the accuracy of the component modelling and definitions of the boundary conditions becomes more important. One such component is the ball bearing which consist of several parts and has a nonlinear behavior where the balls are in contact with the rings.

    The task given was to develop new methods to model roller bearings in Siemens finite element modelling software NX Nastran. Then conduct a strain measurement, to compare the methods to real experimental values. The goal with the report is to find one or more methods to model roller bearings, with accurate results, that can beused in their development work.

    The report was conducted by first doing a study on bearings and finite element modeling, and learning to use the software NX Nastran. Then the development of the methods were done by generating ideas for bearing models and testing them on simple structures. Nine methods was produced and a tenth, the method used to model bearings today, was used as a reference. The methods was used to build bearing models in a finite element model of a six axis robot wrist.

    Simulations were done on the models with different load cases and the results were compared to a strain measurement of the wrists real counterpart. Only six of the models were analyzed in the result, since four of the models returned results that were deemed unusable.

    When compiling the result data no model was found to accurately recreate the stresses in every load case. Three methods, that allow deformation, performed similarly. One of them is suggested to be used as modelling method in the future. Worst of the methods, according to the results compiled, was found to be the method used today. It fails to describe local stresses around the bearing. For continued work it is suggested that linear contact elements is studied further. Four out of five models constructed with linear contact elements failed to return satisfactory results.

  • 55.
    Adolfsson, Joakim
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Characterization of combinatorial Cu2ZnSnS4 thin films2018Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The kesterite Cu2ZnSnS4 (CZTS) is considered as a possible absorber layer in future photovoltaic (PV) applications. The abundance of its constituent elements along with the material being non-toxic and having a direct band gap of around 1.5 eV make it an attractive material for solar cell applications. So far, cells with an efficiency of 12.6 % have been achieved. The limiting factor is the finished cells' open circuit voltage (VOC) deficit which has been attributed to structural defects in the material. Problems with sustaining a sulfur-enriched atmosphere during the annealing step of material production have been observed, and are thought to be partially responsible for the high density of structural defects. Elemental sulfur is commonly used for inducing a sulfur-enriched atmosphere in the anneal. In this study, four combinatorial and polycrystalline CZTS thin films were prepared and annealed in different conditions with regards to time, sulfur source and amount. The samples were characterized using energy dispersive-, Raman- and photoluminescence spectroscopy. The effect of the anneal on the different composition regions were analyzed and secondary phases were identified. Introducing CuS as the sulfur source during the anneal reduced the decomposition of the CZTS phase, and lowered the density of the defect complex [ZnCu + CuZn], while enlarging the single phase region. Strictly and highly Sn-rich compositions of CZTS was observed to yield both high cation order and photoluminescence intensity, and a link between the two parameters was observed.

  • 56.
    Adrian, Ehrnebo
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Elektricitetslära.
    Single Crystalline CVD Diamond Based Devices for Power Electronics Applications2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Chemical vapor deposited single-crystalline diamond has rare material properties such as thermal conductivity five times as high as copper, a wide band gap, a high breakdown field and high carrier mobilities. This makes it a very interesting material for high power, high frequency and high temperature applications.

    In this thesis work, metal oxide semiconductor (MOS) capacitors of diamond substrate were fabricated and analyzed. The MOS capacitor is a building block of the metal oxide semiconductor field effect transistor (MOSFET). Capacitance-voltage (C-V) measurements can provide useful information of the operation of a MOS. Electrical characterization by C-V and current-voltage (I-V) measurements at temperatures ranging from 20 to 150 degrees Celsius were performed on the MOS capacitors to examine flatband and threshold voltages, oxide charge, and oxide thickness.

    At elevated temperatures, low frequency C-V curves with threshold voltages of approximately 5 V were obtained for MOS capacitors consisting of aluminum gates, a 30 nm layer of aluminum oxide, and boron doped diamond with acceptor concentration 3.1 x 1017 cm-3. The C-V measurements also showed large variations in flatband voltage for different contacts of the MOS capacitor, indicating the presence of oxide charge. Oxide thickness was also extracted from the C-V measurements, typically showing thicknesses around 15-19 nm.

    Also in this  thesis, an alternative method for reducing the electric field strength around the edges of the contact of a Schottky diode has been examined. This method consists of alternating the geometry by etching the semiconductor where the contact is to be placed. Simulations performed in Comsol Multiphysics showed that a reduction of the field strength of approximately 30 % at the contacts could be achieved by etching the substrate.

  • 57.
    Adsten, Monika
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Materialvetenskap.
    Solar Thermal Collectors at High Latitudes: Design and performance of non-tracking concentrators2002Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Solar thermal collectors at high latitudes have been studied, with emphasis on concentrating collectors. A novel design of concentrating collector, the Maximum Reflector Collector (MaReCo), especially designed for high latitudes, has been investigated optically and thermally. The MaReCo is an asymmetrical compound parabolic concentrator with a bi-facial absorber. The collector can be adapted to various installation conditions, for example stand-alone, roof- or wall mounted. MaReCo prototypes have been built and outdoor-tested. The evaluation showed that all types work as expected and that the highest annually delivered energy output, 340 kWh/m2, is found for the roof MaReCo. A study of the heat-losses from the stand-alone MaReCo lead to the conclusion that teflon transparent insulation should be placed around the absorber, which decreases the U-value by about 30%.

    A method was developed to theoretically study the projected radiation distribution incident on the MaReCo bi-facial absorber. The study showed that the geometry of the collectors could be improved by slight changes in the acceptance intervals. It also indicated that the MaReCo design concept could be used also at mid-European latitudes if the geometry is changed.

    A novel method was used to perform outdoor measurements of the distribution of concentrated light on the absorber and then to calculate the annually collected zero-loss energy, Ea,corr, together with the annual optical efficiency factor. A study using this method indicated that the absorber should be mounted along the 20º optical axis instead of along the 65º optical axis, which leads to an increase of about 20% in Ea,corr. The same absorber mounting is suggested from heat loss measurements. The Ea,corr at 20º absorber mounting angle can be increased by 5% if the absorber fin thickness is changed from 0.5 to 1 mm and by 13% if two 71.5 mm wide fins are used instead of one that is 143 mm wide. If the Ea,corr for the standard stand-alone MaReCo with 143 mm wide absorber mounted at 65º is compared to that of a collector with a 71.5 mm wide absorber mounted at 20º, the theoretical increase is 38%.

    Delarbeten
    1. Evaluation of CPC-collector designs for stand-alone, roof- or wall installation
    Öppna denna publikation i ny flik eller fönster >>Evaluation of CPC-collector designs for stand-alone, roof- or wall installation
    2005 (Engelska)Ingår i: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 79, nr 6, s. 638-647Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    An asymmetrically truncated non-tracking compound parabolic concentrator type collector design concept has been developed. The collector type has a bi-facial absorber and is optimised for northern latitudes. The concept is based on a general reflector form that is truncated to fit different installation conditions. In this paper collectors for stand-alone, roof and wall mounting are studied. Prototypes of six different collectors have been built and outdoor tested. The evaluation gave high annual energy outputs for a roof mounted collector, 925 MJ/m2, and a stand-alone collector with Teflon, 781 MJ/m2, at an operating temperature of Top = 75 °C. A special design for roofs facing east or west was also investigated and gave an annual energy output of 349 (east) and 436 (west) MJ/m2 at Top = 75 °C. If a high solar fraction over the year is the objective, a load adapted collector with a high output during spring/fall and a low output during summer can be used. Such a collector had an output of 490 MJ/m2 at Top = 75 °C. Finally a concentrating collector for wall mounting was evaluated with an estimated annual output of 194 MJ/m2 at Top = 75 °C. The concentrator design concept can also be used for concentrators for PV-modules.

    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:uu:diva-89748 (URN)10.1016/j.solener.2005.04.023 (DOI)
    Tillgänglig från: 2002-04-05 Skapad: 2002-04-05 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    2. Calorimetric measurements of heat losses from a truncated asymmetric solar thermal concentrator
    Öppna denna publikation i ny flik eller fönster >>Calorimetric measurements of heat losses from a truncated asymmetric solar thermal concentrator
    2002 (Engelska)Ingår i: Solar EnergyArtikel i tidskrift (Refereegranskat) Submitted
    Identifikatorer
    urn:nbn:se:uu:diva-89749 (URN)
    Tillgänglig från: 2002-04-05 Skapad: 2002-04-05 Senast uppdaterad: 2009-04-29Bibliografiskt granskad
    3. Annually projected solar radiation distribution analysis for optimum design of asymmetric CPC
    Öppna denna publikation i ny flik eller fönster >>Annually projected solar radiation distribution analysis for optimum design of asymmetric CPC
    2002 (Engelska)Ingår i: Solar EnergyArtikel i tidskrift (Refereegranskat) Submitted
    Identifikatorer
    urn:nbn:se:uu:diva-89750 (URN)
    Tillgänglig från: 2002-04-05 Skapad: 2002-04-05 Senast uppdaterad: 2009-04-29Bibliografiskt granskad
    4. Measurement of radiation distribution on the absorber in an asymmetric CPC collector
    Öppna denna publikation i ny flik eller fönster >>Measurement of radiation distribution on the absorber in an asymmetric CPC collector
    2004 (Engelska)Ingår i: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 76, nr 1-3, s. 199-206Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    A method to estimate the annual collected energy and the annual average optical efficiency factor is suggested. The radiation distribution on the absorber of an asymmetric CPC collector with a flat bi-facial absorber is measured for three different absorber mounting angles using a photo diode. The annual optical efficiency factors and a relative measure of the annual collected energy are determined for collectors with the absorber fin thickness 0.5 and 1 mm, and for a collector with a teflon convection suppression film mounted around the absorber. With the local optical efficiency factors and the annual incident solar energy distribution considered, the analysis indicates that the energy gain for a mounting angle of 20° is higher than for a collector with 65° absorber mounting angle. The annual collected energy is increased with 6–8% if the absorber fin thickness is increased from 0.5 to 1 mm. The annual average optical efficiency factor is relatively independent of the absorber mounting angle. It was found to be 0.87–0.88 for a collector with a 0.5 mm thick absorber fin and 0.92 for a collector with a 1 mm thick absorber fin or for a collector with 0.5 mm thick absorber fin with a teflon convection suppression film added. The low annual average optical efficiency factor is not caused by the uneven irradiance distribution but by the relatively high UL-values.

    Nationell ämneskategori
    Naturvetenskap
    Identifikatorer
    urn:nbn:se:uu:diva-89751 (URN)10.1016/j.solener.2003.08.024 (DOI)
    Konferens
    Solar World Congress 2001
    Tillgänglig från: 2002-04-05 Skapad: 2002-04-05 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    5. Comparison of the optical efficiency of a wide and a narrow absorber fin in an asymmetric concentrating collector
    Öppna denna publikation i ny flik eller fönster >>Comparison of the optical efficiency of a wide and a narrow absorber fin in an asymmetric concentrating collector
    (Engelska)Manuskript (Övrig (populärvetenskap, debatt, mm))
    Identifikatorer
    urn:nbn:se:uu:diva-89752 (URN)
    Tillgänglig från: 2002-04-05 Skapad: 2002-04-05 Senast uppdaterad: 2010-01-14Bibliografiskt granskad
    6. The influence of climate and location on collector performance
    Öppna denna publikation i ny flik eller fönster >>The influence of climate and location on collector performance
    2002 (Engelska)Ingår i: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 25, nr 4, s. 499-509Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    The influence of annual climate variations on the performance of solar thermal collectors in the northern part of Europe has been investigated. The annual solar collector energy output has been calculated with the MINSUN simulation program using hourly, measured climatic data for the years 1983–98 for three cities situated in the south (Lund), central (Stockholm) and north (Luleå) of Sweden. A synthetic year created with the Meteonorm weather simulation program was also used in the simulations. Two solar thermal collectors were modelled: a flat plate solar collector and a tubular vacuum collector, both of commercial standard.

    The thermal energy output is strongly correlated to the annual global irradiation at a horizontal surface. The annual average energy delivered from the flat plate collector was 337 kWh/m2 for Stockholm (337 for Lund and 298 for Luleå), and from the vacuum tube collector 668 kWh/m2 for Stockholm (675 for Lund and 631 for Luleå) at an operating temperature of T=50°C. Maximum deviations from the average value for this 16-year period are around 20% for the flat plate and 15% for the vacuum tube collector, at T=50°C.

    The relation between global irradiation on a horizontal surface and the annually collected thermal energy at a constant operating temperature could be fitted to a linear equation: qu=aG(0°)+bT, where qu is the energy output from the collector, G(0°) the global irradiation at a horizontal surface, T the average temperature of the collector fluid, and a and b fitting parameters in a double linear regression analysis.

    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:uu:diva-89753 (URN)10.1016/S0960-1481(01)00091-X, (DOI)
    Tillgänglig från: 2002-04-05 Skapad: 2002-04-05 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
    7. Simulation of the influence of tilt and azimuth angles on the collector output of solar collectors at northern latitudes
    Öppna denna publikation i ny flik eller fönster >>Simulation of the influence of tilt and azimuth angles on the collector output of solar collectors at northern latitudes
    1999 (Engelska)Ingår i: Proceedings North Sun conference 1999, Edmonton CanadaArtikel i tidskrift (Refereegranskat) Accepted
    Identifikatorer
    urn:nbn:se:uu:diva-89754 (URN)
    Tillgänglig från: 2002-04-05 Skapad: 2002-04-05 Senast uppdaterad: 2009-04-29Bibliografiskt granskad
    8. The impact of optical and thermal properties on the performance of flat plate solar collectors
    Öppna denna publikation i ny flik eller fönster >>The impact of optical and thermal properties on the performance of flat plate solar collectors
    Visa övriga...
    2000 (Engelska)Ingår i: Proceedings Eurosun 2000, Copenhagen, DenmarkArtikel i tidskrift (Refereegranskat) Published
    Identifikatorer
    urn:nbn:se:uu:diva-89755 (URN)
    Tillgänglig från: 2002-04-05 Skapad: 2002-04-05 Senast uppdaterad: 2009-04-29Bibliografiskt granskad
    9. Optical scattering from rough aluminum surfaces
    Öppna denna publikation i ny flik eller fönster >>Optical scattering from rough aluminum surfaces
    Visa övriga...
    2001 (Engelska)Ingår i: J. Applied Optics, Vol. 40, s. 2148-2158Artikel i tidskrift (Refereegranskat) Published
    Identifikatorer
    urn:nbn:se:uu:diva-89756 (URN)
    Tillgänglig från: 2002-04-05 Skapad: 2002-04-05 Senast uppdaterad: 2009-04-29Bibliografiskt granskad
    10. Optical characterization of industrially sputtered nickel-nickel oxide solar selective surface
    Öppna denna publikation i ny flik eller fönster >>Optical characterization of industrially sputtered nickel-nickel oxide solar selective surface
    2000 (Engelska)Ingår i: Solar Energy, Vol. 68, s. 325-328Artikel i tidskrift (Refereegranskat) Published
    Identifikatorer
    urn:nbn:se:uu:diva-89757 (URN)
    Tillgänglig från: 2002-04-05 Skapad: 2002-04-05 Senast uppdaterad: 2009-04-29Bibliografiskt granskad
  • 58.
    Adsten, Monika
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Materialvetenskap.
    Helgesson, Anna
    Karlsson, Björn
    Evaluation of CPC-collector designs for stand-alone, roof- or wall installation2005Ingår i: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 79, nr 6, s. 638-647Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An asymmetrically truncated non-tracking compound parabolic concentrator type collector design concept has been developed. The collector type has a bi-facial absorber and is optimised for northern latitudes. The concept is based on a general reflector form that is truncated to fit different installation conditions. In this paper collectors for stand-alone, roof and wall mounting are studied. Prototypes of six different collectors have been built and outdoor tested. The evaluation gave high annual energy outputs for a roof mounted collector, 925 MJ/m2, and a stand-alone collector with Teflon, 781 MJ/m2, at an operating temperature of Top = 75 °C. A special design for roofs facing east or west was also investigated and gave an annual energy output of 349 (east) and 436 (west) MJ/m2 at Top = 75 °C. If a high solar fraction over the year is the objective, a load adapted collector with a high output during spring/fall and a low output during summer can be used. Such a collector had an output of 490 MJ/m2 at Top = 75 °C. Finally a concentrating collector for wall mounting was evaluated with an estimated annual output of 194 MJ/m2 at Top = 75 °C. The concentrator design concept can also be used for concentrators for PV-modules.

  • 59.
    Adsten, Monika
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Materialvetenskap.
    Hellström, Bengt
    Karlsson, Björn
    Comparison of the optical efficiency of a wide and a narrow absorber fin in an asymmetric concentrating collectorManuskript (Övrig (populärvetenskap, debatt, mm))
  • 60.
    Adsten, Monika
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Materialvetenskap.
    Hellström, Bengt
    Karlsson, Björn
    Measurement of radiation distribution on the absorber in an asymmetric CPC collector2004Ingår i: Solar Energy, ISSN 0038-092X, E-ISSN 1471-1257, Vol. 76, nr 1-3, s. 199-206Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method to estimate the annual collected energy and the annual average optical efficiency factor is suggested. The radiation distribution on the absorber of an asymmetric CPC collector with a flat bi-facial absorber is measured for three different absorber mounting angles using a photo diode. The annual optical efficiency factors and a relative measure of the annual collected energy are determined for collectors with the absorber fin thickness 0.5 and 1 mm, and for a collector with a teflon convection suppression film mounted around the absorber. With the local optical efficiency factors and the annual incident solar energy distribution considered, the analysis indicates that the energy gain for a mounting angle of 20° is higher than for a collector with 65° absorber mounting angle. The annual collected energy is increased with 6–8% if the absorber fin thickness is increased from 0.5 to 1 mm. The annual average optical efficiency factor is relatively independent of the absorber mounting angle. It was found to be 0.87–0.88 for a collector with a 0.5 mm thick absorber fin and 0.92 for a collector with a 1 mm thick absorber fin or for a collector with 0.5 mm thick absorber fin with a teflon convection suppression film added. The low annual average optical efficiency factor is not caused by the uneven irradiance distribution but by the relatively high UL-values.

  • 61.
    Adsten, Monika
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Materialvetenskap.
    Joerger, Ralph
    Järrendahl, Kenneth
    Wäckelgård, Ewa
    Optical characterization of industrially sputtered nickel-nickel oxide solar selective surface2000Ingår i: Solar Energy, Vol. 68, s. 325-328Artikel i tidskrift (Refereegranskat)
  • 62.
    Adsten, Monika
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Materialvetenskap.
    Karlsson, Björn
    Annually projected solar radiation distribution analysis for optimum design of asymmetric CPC2002Ingår i: Solar EnergyArtikel i tidskrift (Refereegranskat)
  • 63.
    Adsten, Monika
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Materialvetenskap.
    Perers, Bengt
    Simulation of the influence of tilt and azimuth angles on the collector output of solar collectors at northern latitudes1999Ingår i: Proceedings North Sun conference 1999, Edmonton CanadaArtikel i tidskrift (Refereegranskat)
  • 64.
    Adsten, Monika
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Materialvetenskap.
    Perers, Bengt
    Wäckelgård, Ewa
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper.
    The influence of climate and location on collector performance2002Ingår i: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 25, nr 4, s. 499-509Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of annual climate variations on the performance of solar thermal collectors in the northern part of Europe has been investigated. The annual solar collector energy output has been calculated with the MINSUN simulation program using hourly, measured climatic data for the years 1983–98 for three cities situated in the south (Lund), central (Stockholm) and north (Luleå) of Sweden. A synthetic year created with the Meteonorm weather simulation program was also used in the simulations. Two solar thermal collectors were modelled: a flat plate solar collector and a tubular vacuum collector, both of commercial standard.

    The thermal energy output is strongly correlated to the annual global irradiation at a horizontal surface. The annual average energy delivered from the flat plate collector was 337 kWh/m2 for Stockholm (337 for Lund and 298 for Luleå), and from the vacuum tube collector 668 kWh/m2 for Stockholm (675 for Lund and 631 for Luleå) at an operating temperature of T=50°C. Maximum deviations from the average value for this 16-year period are around 20% for the flat plate and 15% for the vacuum tube collector, at T=50°C.

    The relation between global irradiation on a horizontal surface and the annually collected thermal energy at a constant operating temperature could be fitted to a linear equation: qu=aG(0°)+bT, where qu is the energy output from the collector, G(0°) the global irradiation at a horizontal surface, T the average temperature of the collector fluid, and a and b fitting parameters in a double linear regression analysis.

  • 65.
    Adsten, Monika
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Materialvetenskap.
    Wäckelgård, Ewa
    Karlsson, Björn
    Calorimetric measurements of heat losses from a truncated asymmetric solar thermal concentrator2002Ingår i: Solar EnergyArtikel i tidskrift (Refereegranskat)
  • 66.
    af Ekenstam, Love
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Signaler och System.
    Modellering av signalbehandlingen i ett cochleaimplantat och utvärdering av modellen.2014Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Ett program som simulerar signalbehandlingen i ett cochleaimplantat med signalbehandlingsstrategin ACE (Advanced Combined Encoder) har konstruerats. Programmets främsta syfte är att i förväg prova ut inställningar i ett cochleaimplantat och genom detta försöka förutsäga olika användares individuella inställningar.

     

    Programmet har validerats med utsignaler bearbetade av Cochlear Limited i deras egenkonstruerade Matlab-modul för forskning inom cochleaimplantat, NMT (Nucleus Matlab Toolbox). Samma insignal som använts av Cochlear Limited har processats av programmet och utsignalerna från detta jämfördes med utsignalerna från NMT. De bägge utsignalerna, producerade med samma inställningar, stämde bra överens.

     

    Komprimeringsfunktionen i programmet, som är en vital del av signalbehandlingen, visade sig stämma bra överens med NMT:s komprimeringsfunktion, sånär som på en relativ minskning av värdet vid starka insignaler. Programmet ska nu användas på Cochleaimplantat-sektionen vid Uppsala Akademiska sjukhus för att pröva ut individuella inställningar till användare av cochleaimplantat. Förhoppningen är att bättre inställningar ska leda till bättre talförståelse och i förlängningen, bättre upplevelse av musik.

  • 67.
    Afshar, R
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    van Dijk, N.P.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Bjurhager, Ingela
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Gamstedt, E. Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Comparison of experimental testing and finite element modelling of a replica of a section of the Vasa warship to identify the behaviour of structural joints2017Ingår i: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 147, s. 62-76Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Modelling in design of new support systems necessitates the joint stiffness of the existing wooden structures. In valuable structures, e.g. in cultural heritage, or structures with inaccessible joints, these stiffness values must be estimated, e.g. by testing joints in tailored replicas of the original parts. Although a simplified structure, the replica, can call for finite element (FE) modelling to capture the stiffness parameters. The first step in such a process is to compare FE predictions with experimental tests, for validation purposes. The reasons for unavoidable differences in load-displacement behaviour between model predictions and experimental test should be identified, and then possibly remedied by an improved model. Underlying causes like the complex shape of joints, geometrical uncertainties, contact mechanisms and material nonlinearity are generally too computationally expensive to be included in a full-scale model. It is therefore convenient to collect such effects in the contact penalty stiffness in the joint contact areas where stresses are high, which influences the resulting joint stiffness. A procedure for this is here illustrated for the case of the 17th century Vasa shipwreck A replica of a section of the ship has been constructed, and its joints were tested in bending-compression, in-plane shear and rotation. The FE simulations showed stiffer behaviour than the experimental results. Therefore, a normal penalty stiffness in contact surfaces of the joint were introduced, and used as a calibration parameter to account for the simplifying assumptions or indeliberate imprecision in the model, e.g. concerning boundary conditions, material properties and geometrical detail. The difference between numerical predictions and experimental results could then be significantly reduced, with a suitable normal penalty stiffness value. Once an acceptable finite element model has been obtained, it is shown how this can be used to identify stiffness values for joints in the physical structure with compensation for degradation of material properties due to aging and conservation treatment.

  • 68.
    Afshar, Reza
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Ahlgren, Anders
    Vasa museum.
    Gamstedt, E. Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Characterization of mechanical properties of Vasa oak and their application in a full-scale numerical model for support assessment2019Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The 17th century Vasa shipwreck is a well-known object of cultural heritage. According to geodetic measurements inside and outside of the ship as well as on the support structure, the ship is sinking onto its cradle. The analysis of measurements showed the ship undergoes continued deformation with increasing strain. Previous research projects on the Vasa ship have largely been focused on the chemical degradation of the Vasa oak, which concerns the waterlogged polyethylene glycol (PEG) impregnated oak wood. The main goal was to provide understanding of the degradation mechanisms and possible remedies to mitigate the chemical decay. In this paper, a review is presented of previous research in term of characterization of mechanical properties, and effects of PEG and moisture on the mechanical behaviour of the Vasa oak. In addition, a full-scale finite-element model of the Vasa ship has been developed to assess its current and future structural behaviour, as well as a tool to design an improved support structure. The mechanical properties, defined in the model in terms of orthotropic elastic engineering constants, have been determined in previous work. Moreover, creep properties of the archaeological wood material have been and are being characterized, so that the model can be extended by extrapolation to predict future deformation. Geodetic measurements have been used for validation of the static model. The approach undertaken in this project could hopefully be useful in design strategies of improved support for other aging and deforming wood structures in cultural heritage.

  • 69.
    Afshar, Reza
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Alavyoon, Navid
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Mikrosystemteknik.
    Ahlgren, Anders
    Swedish National Maritime Museums, the Vasa Museum.
    van Dijk, Nico P.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Vorobyev, Alexey
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Gamstedt, Kristofer
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    A full-scale finite-element model of the Vasa ship2017Ingår i: Proceedings of ECCOMAS Thematic Conference CompWood 2017: Computational Methods in Wood Mechanics, 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    A full-scale model of the 17th century Vasa shipwreck has been developed to assess its current and future structural stability as well as design an improved support structure. A wireframe model, consisting of only lines, points and curves to describe the geometry of the ship, has been provided by the Vasa museum. It has been developed based on geodetic measurements using a total station. From this wireframe model, a three-dimensional (3D) model comprising solid bodies for solid-like parts (i.e. hull and keel), surfaces for the shell-like components (deck planks) and lines for beam-like constituents (deck beams) has been developed in Creo Parametric 3D software. This geometric model has been imported in finite-element software, Ansys, for further development of the stiffeners (knees, riders, stanchions, masts, etc.), adjustment of the correct location of deck beams and, finally, structural analyses of the entire ship (Figure 1). The procedure for selection of the different types of elements in the finite-element (FE) model, the definition of orthotropic material properties for the timber structure and preliminary results are discussed in this paper. Experiences drawn from this engineering project may also be useful in development of finite element models for structural assessment of other complex wooden structures in cultural heritage.

  • 70.
    Aggarwal, Shubhesh
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Industriell teknik.
    Kaldi, Kjzal
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Industriell teknik.
    Agile Project Management for Knowledge-Based Projects in Manufacturing Industry: Case Study: Epiroc Drilling Tools, Fagersta, Sweden2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Epiroc Drilling Tools is a manufacturing company that produces tools for rock mining and excavation. The company adopted the principles and framework of Lean Product Development in their R&D department with few practices of an agile framework called Scrum. These agile practices are used in the pre-study phase or the knowledge value stream of their lean product development. Hence, this research is limited to the knowledge value stream within the R&D department.

    The use of agile project management in manufacturing industry is unique and majority of the agile frameworks are specifically designed to suit the needs of software development companies. Several theories like Scrum, Lean, Kanban and DSDM were studied by the researchers to scrutinize the current framework of the department. The challenges and the similarities of the currently used framework with several other agile frameworks and the companies are discussed. Several qualitative research methods were adopted to know the viewpoints of the working employees in the department which are compared with other companies like Volvo Cars, ABB, LShift, EnergySoftware and from another division of Epiroc called Rocktec Automation who faced some similar challenges while practicing agile project management. After further research on the theories and comparison of the process, roles of the working employees and documentations within the knowledge value stream, DSDM had more similarities with the currently used framework than Scrum. This allowed to recommend ways that can fill the missing gaps using practices of DSDM without altering the existing working procedure in the knowledge value stream. This ensures that the improvement in the knowledge value stream remains continuous. On the contrary, a brief discussion is included on whether there is a need to be agile for manufacturing industries or is it just a changing trend in the field of project management.

  • 71.
    Agrawal, Piyush
    et al.
    United Technologies Research Center, Cork, Irland.
    Ahlén, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Signaler och System.
    Olofsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Signaler och System.
    Gidlund, M
    Characterization of long term channel variations in industrial wireless sensor networks2014Konferensbidrag (Refereegranskat)
  • 72.
    Agrawal, Piyush
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Signaler och System.
    Ahlén, Anders
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Signaler och System.
    Olofsson, Tomas
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Signaler och System.
    Gidlund, Mikael
    Long Term Channel Characterization for Energy Efficient Transmission in Industrial Environments2014Ingår i: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 62, nr 8, s. 3004-3014Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    One of the challenges for a successful use of wireless sensor networks in process industries is to design networks with energy efficient transmission, to increase the lifetime of the deployed network while maintaining the required latency and bit-error rate. The design of such transmission schemes depend on the radio channel characteristics of the region. This paper presents an investigation of the statistical properties of the radio channel in a typical process industry, particularly when the network is meant to be deployed for a long time duration, e. g., days, weeks, and even months. Using 17-20-h-long extensive measurement campaigns in a rolling mill and a paper mill, we highlight the non-stationarity in the environment and quantify the ability of various distributions, given in the literature, to describe the variations on the links. Finally, we analyze the design of an optimal received signal-to-noise ratio (SNR) for the deployed nodes and show that improper selection of the distribution for modeling of the variations in the channel can lead to an overuse of energy by a factor of four or even higher.

  • 73.
    Agthe, Michael
    et al.
    Stockholm Univ, Arrhenius Lab, Dept Mat & Environm Chem, SE-10691 Stockholm, Sweden..
    Wetterskog, Erik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets fysik.
    Bergström, Lennart
    Stockholm Univ, Arrhenius Lab, Dept Mat & Environm Chem, SE-10691 Stockholm, Sweden..
    Following the Assembly of Iron Oxide Nanocubes by Video Microscopy and Quartz Crystal Microbalance with Dissipation Monitoring2017Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 33, nr 1, s. 303-310Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have studied the growth of ordered arrays by evaporation-induced self-assembly of iron oxide nanocubes with edge lengths of 6.8 and 10.1 nm using video microscopy (VM) and quartz crystal microbalance with dissipation monitoring (QCM-D). Ex situ electron diffraction of the ordered arrays demonstrates that the crystal axes of the nanocubes are coaligned and confirms that the ordered arrays are mesocrystals. Time-resolved video microscopy shows that growth of the highly ordered arrays at slow solvent evaporation is controlled by particle diffusion and can be described by a simple growth model. The growth of each mesocrystal depends only on the number of nanoparticles within the accessible region irrespective of the relative time of formation. The mass of the dried mesocrystals estimated from the analysis of the bandwidth-shift-to-frequency-shift ratio correlates well with the total mass of the oleate-coated nanoparticles in the deposited dispersion drop.

  • 74. Ahl, Martin
    et al.
    Bergman, Stefan
    Bergström, Ulf
    Eliasson, Thomas
    Ripa, Magnus
    Weihed, Pär
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper. Luleå tekniska universitet, Geovetenskap och miljöteknik.
    Geochemical classification of plutonic rocks in central and northern Sweden2001Rapport (Övrigt vetenskapligt)
  • 75.
    Ahl, Philip
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper.
    Johansson Norman, Simon
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper.
    Projekt inom framkopplat aktivt brusreduceringssystem2017Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
  • 76.
    Ahlberg, Johan
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper.
    Georges, Elza
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper.
    Norlén, Mikael
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper.
    The potential of hemp buildings in different climates: A comparison between a common passive house and the hempcrete building system2014Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The aim of this bachelor thesis was to study the potential of hemp buildings in different climates. The report examines and models two different energy efficient building concepts – the more common passive house and the environmental friendly hempcrete building system. These two buildings thermal performances were then simulated and compared in different climates followed by a brief discussion about their economic and environmental impact.

    The simulation was performed with the energy calculating program VIP-energy v 2.1.1 with the two models located in Kiruna, Sundsvall, Malmo, Berlin and Rome to represent the different climates. Simulations for different wall sizes and a sensitivity analysis of some significant parameters were also made.

    The hempcrete building system showed to have a thermal performance similar to that of passive houses in more southern climates. In the north of Sweden however the hempcrete building required up to 20 % more energy than the passive house to maintain comfortable indoor temperatures. This deficit could be compensated for with hemp fibre insulation to augment the building envelope and U-value. Furthermore the hygrothermal material properties that were not included in the simulation can be expected to have a significant positive impact on hemp buildings relative thermal performance.

    With a passive house thermal performance, a healthy indoor environment and an economically viable and environmental friendly production process hemp building demonstrated great potential in all the fields studied.

  • 77.
    Ahlberg, Mats
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Industriell teknik.
    Kostnadseffektiv IT-leverans: IT Financial Management hos bank- och försäkringsbolaget Skandia2011Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    IT-organisationer börjar ta större och större plats i bolags affärsverksamhet, och är idag även en av de största kostnadsposterna. I samband med detta ökar kraven på den IT som levereras där bland annat fler vill ha bättre insyn i vad som levereras och hur mycket leveransen kostar. Detta behov av insyn återfinns både hos IT-leverantören och hos deras kunder. Problem finns emellertid att göra IT mätbart i finansiella termer.  IT Financial Management (ITFM) är ännu i sin linda, men är en arbetsprocess som tar sig an denna problematik; Att kunna ge finansiell data på IT-tjänster. ITFM är en del av det vidare begreppet IT Service Management, vilket syftar till att beskriva hur IT som tjänst levereras på bästa sätt till en kund.  

    Denna uppsats undersöker hur IT Financial Management bedrivs hos bank- och försäkringsbolaget Skandias interna IT-leverantör Skandia IT Services (SITS), och hur dessa skulle vilja att denna verksamhets bedrivs framöver. Uppsatsen undersöker också om det finns stödverktyg som skulle kunna hjälpa dem att nå sin uppsatta ITFM-vision. Detta görs genom en undersökning av två verktyg; Service-Now.Com, och Digital Fuel. Dessa verktyg jämförs i hur bra de kan möta SITS identifierade behov, och hur mycket ett ägarskap skulle kosta dem. Undersökningen visar att Digital Fuel kan möta uppsatta krav bättre, men att Service-Now.Com kan göra nästan lika mycket till en lägre kostnad. Detta leder till att denna uppsats anser att Service-Now.Com möter Skandias behov bäst.  

    Rapporten bygger på teorier och intervjuer. Teorierna behandlar Service Management, IT Financial Management, modeller för val av stödverktyg, och deras kostnader. Intervjuerna skedde dels med personal hos SITS, dels med leverantörerna av stödverktygen. Dessa – teorierna och resultaten från intervjuer - är sedan sammanförda i en analys som diskuterar hur ett stödverktyg skulle kunna hjälpa SITS i deras framtida ITFM-arbete genom att underlätta en stor del av det interna arbetet, samt kunna hjälpa till att underlätta för Skandias resterande affärsverksamhet genom att bidra med information som gör IT-organisationen mer transparent och mätbar. Ett verktyg som stöd kan också hjälpa till att redogöra för hur mycket olika delar av IT kostar, vad som bygger dessa kostnader, och vilken affärsnytta som IT-leveransen genererar. Detta skulle kunna underlätta beslutsfattande och analys av den finansiella situationen kring IT, vilka är problem som SITS ser i deras nuvarande arbetssätt.

  • 78.
    Ahlberg, Patrik
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Graphene Implementation Study in Semiconductor Processing2016Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Graphene, with its two-dimensional nature and unique properties, has for over a decade captured enormous interests in both industry and academia. This work tries to answer the question of what would happen to graphene when it is subjected to various processing conditions and how this would affect the graphene functionality. The focus is placed on its ability to withstand different thin-film deposition environments with regard to the implementation of graphene in two application areas: as a diffusion barrier and in electronic devices.

    With single-layer graphene films grown in-house by means of chemical vapor deposition (CVD), four techniques among the well-established thin-film deposition methods are studied in detail: atomic layer deposition (ALD), evaporation, sputter-deposition and spray-deposition. And in this order, these methods span a large range of kinetic impact energies from low to high. Graphene is known to have a threshold displacement energy of 22 eV above which carbon atoms are ejected from the lattice. Thus, ALD and evaporation work with energies below this threshold, while sputtering and spraying may involve energies above. The quality of the graphene films undergone the various depositions is mainly evaluated using Raman spectroscopy.

    Spray deposition of liquid alloy Ga-In-Sn is shown to require a stack of at least 4 layers of graphene in order to act as an effective barrier to the Ga diffusion after the harsh spray-processing. Sputter-deposition is found to benefit from low substrate temperature and high chamber pressure (thereby low kinetic impact energy) so as to avoid damaging the graphene. Reactive sputtering should be avoided. Evaporation is non-invasiveness with low kinetic impact energy and graphene can be subjected to repeated evaporation and removal steps without losing its integrity. With ALD, the effects on graphene are of different nature and they are investigated in the field-effect-transistor (FET) configuration. The ALD process for deposition of Al2O3 films is found to remove undesired dopants from the prior processing and the Al2O3 films are shown to protect the graphene channel from doping by oxygen. When the substrate is turned hydrophobic by chemical treatment prior to graphene transfer-deposition, a unipolar transistor behavior is obtained.

    Delarbeten
    1. A two-in-one process for reliable graphene transistors processed with photolithography
    Öppna denna publikation i ny flik eller fönster >>A two-in-one process for reliable graphene transistors processed with photolithography
    Visa övriga...
    2015 (Engelska)Ingår i: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, nr 20, artikel-id 203104Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    Research on graphene field-effect transistors (GFETs) has mainly relied on devices fabricated using electron-beam lithography for pattern generation, a method that has known problems with polymer contaminants. GFETs fabricated via photo-lithography suffer even worse from other chemical contaminations, which may lead to strong unintentional doping of the graphene. In this letter, we report on a scalable fabrication process for reliable GFETs based on ordinary photo-lithography by eliminating the aforementioned issues. The key to making this GFET processing compatible with silicon technology lies in a two-in-one process where a gate dielectric is deposited by means of atomic layer deposition. During this deposition step, contaminants, likely unintentionally introduced during the graphene transfer and patterning, are effectively removed. The resulting GFETs exhibit current-voltage characteristics representative to that of intrinsic non-doped graphene. Fundamental aspects pertaining to the surface engineering employed in this work are investigated in the light of chemical analysis in combination with electrical characterization.

    Nationell ämneskategori
    Fysik Teknik och teknologier
    Identifikatorer
    urn:nbn:se:uu:diva-269191 (URN)10.1063/1.4935985 (DOI)000365688700049 ()
    Forskningsfinansiär
    Knut och Alice Wallenbergs Stiftelse, 2011.0113, 2011.0082Stiftelsen för strategisk forskning (SSF), SE13-0061Vetenskapsrådet, 621-2014-5591
    Tillgänglig från: 2015-12-14 Skapad: 2015-12-14 Senast uppdaterad: 2017-12-01Bibliografiskt granskad
    2. Interface Dependent Effective Mobility in Graphene Field Effect Transistors
    Öppna denna publikation i ny flik eller fönster >>Interface Dependent Effective Mobility in Graphene Field Effect Transistors
    2018 (Engelska)Ingår i: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 47, nr 3, s. 1757-1761Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    By pretreating the substrate of a graphene field-effect transistor (G-FET), a stable unipolar transfer characteristic, instead of the typical V-shape ambipolar behavior, has been demonstrated. This behavior is achieved through functionalization of the SiO2/Si substrate that changes the SiO2 surface from hydrophilic to hydrophobic, in combination with postdeposition of an Al2O3 film by atomic layer deposition (ALD). Consequently, the back-gated G-FET is found to have increased apparent hole mobility and suppressed apparent electron mobility. Furthermore, with addition of a top-gate electrode, the G-FET is in a double-gate configuration with independent top- or back-gate control. The observed difference in mobility is shown to also be dependent on the top-gate bias, with more pronounced effect at higher electric field. Thus, the combination of top and bottom gates allows control of the G-FET's electron and hole mobilities, i.e., of the transfer behavior. Based on these observations, it is proposed that polar ligands are introduced during the ALD step and, depending on their polarization, result in an apparent increase of the effective hole mobility and an apparent suppressed effective electron mobility.

    Nationell ämneskategori
    Teknik och teknologier Elektroteknik och elektronik
    Forskningsämne
    Teknisk fysik med inriktning mot elektronik
    Identifikatorer
    urn:nbn:se:uu:diva-284924 (URN)10.1007/s11664-017-6023-6 (DOI)000424341700002 ()
    Forskningsfinansiär
    Knut och Alice Wallenbergs Stiftelse, 2011.0082Vetenskapsrådet, 2014-5591
    Tillgänglig från: 2016-04-19 Skapad: 2016-04-19 Senast uppdaterad: 2018-04-11Bibliografiskt granskad
    3. Defect formation in graphene during low-energy ion bombardment
    Öppna denna publikation i ny flik eller fönster >>Defect formation in graphene during low-energy ion bombardment
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    2016 (Engelska)Ingår i: APL Materials, ISSN 2166-532X, Vol. 4, nr 4, artikel-id 046104Artikel i tidskrift, Letter (Refereegranskat) Published
    Abstract [en]

    This letter reports on a systematic investigation of sputter induced damage in graphene caused by low energy Ar+ ion bombardment. The integral numbers of ions per area (dose) as well as their energies are varied in the range of a few eV's up to 200 eV. The defects in the graphene are correlated to the dose/energy and different mechanisms for the defect formation are presented. The energetic bombardment associated with the conventional sputter deposition process is typically in the investigated energy range. However, during sputter deposition on graphene, the energetic particle bombardment potentially disrupts the crystallinity and consequently deteriorates its properties. One purpose with the present study is therefore to demonstrate the limits and possibilities with sputter deposition of thin films on graphene and to identify energy levels necessary to obtain defect free graphene during the sputter deposition process. Another purpose is to disclose the fundamental mechanisms responsible for defect formation in graphene for the studied energy range.

    Nationell ämneskategori
    Materialkemi Nanoteknik
    Identifikatorer
    urn:nbn:se:uu:diva-284702 (URN)10.1063/1.4945587 (DOI)000375846100007 ()
    Forskningsfinansiär
    Knut och Alice Wallenbergs Stiftelse, 2011.0082Vetenskapsrådet, 2014-5591 2014-6463
    Tillgänglig från: 2016-04-19 Skapad: 2016-04-19 Senast uppdaterad: 2017-01-25Bibliografiskt granskad
    4. Toward synthesis of oxide films on graphene with sputtering based processes
    Öppna denna publikation i ny flik eller fönster >>Toward synthesis of oxide films on graphene with sputtering based processes
    2016 (Engelska)Ingår i: Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics, ISSN 2166-2746, E-ISSN 2166-2754Artikel i tidskrift (Refereegranskat) Submitted
    Nationell ämneskategori
    Teknik och teknologier
    Identifikatorer
    urn:nbn:se:uu:diva-284706 (URN)
    Externt samarbete:
    Tillgänglig från: 2016-04-19 Skapad: 2016-04-19 Senast uppdaterad: 2017-11-30
    5. Graphene as a Diffusion Barrier in Galinstan-Solid Metal Contacts
    Öppna denna publikation i ny flik eller fönster >>Graphene as a Diffusion Barrier in Galinstan-Solid Metal Contacts
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    2014 (Engelska)Ingår i: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 61, nr 8, s. 2996-3000Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    This paper presents the use of graphene as a diffusion barrier to a eutectic Ga-In-Sn alloy, i.e., galinstan, for electrical contacts in electronics. Galinstan is known to be incompatible with many conventional metals used for electrical contacts. When galinstan is in direct contact with Al thin films, Al is readily dissolved leading to the formation of Al oxides present on the surface of the galinstan droplets. This reaction is monitored ex situ using several material analysis methods as well as in situ using a simple circuit to follow the time-dependent resistance variation. In the presence of a multilayer graphene diffusion barrier, the Al-galinstan reaction is effectively prevented for galinstan deposited by means of drop casting. When deposited by spray coating, the high-impact momentum of the galinstan droplets causes damage to the multilayer graphene and the Al-galinstan reaction is observed at some defective spots. Nonetheless, the graphene barrier is likely to block the formation of Al oxides at the Al/galinstan interface leading to a stable electrical current in the test circuit.

    Nationell ämneskategori
    Annan elektroteknik och elektronik Nanoteknik
    Forskningsämne
    Teknisk fysik med inriktning mot elektronik; Teknisk fysik med inriktning mot mikrosystemteknik
    Identifikatorer
    urn:nbn:se:uu:diva-229503 (URN)10.1109/TED.2014.2331893 (DOI)000342906200056 ()
    Tillgänglig från: 2014-08-10 Skapad: 2014-08-10 Senast uppdaterad: 2017-12-05Bibliografiskt granskad
    6. Scalable residue-free graphene for surface-enhanced Raman scattering
    Öppna denna publikation i ny flik eller fönster >>Scalable residue-free graphene for surface-enhanced Raman scattering
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    2016 (Engelska)Ingår i: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 98, s. 567-571Artikel i tidskrift (Refereegranskat) Published
    Abstract [en]

    A room-temperature polymer-assisted transfer process is developed for large-area, single-layer graphene grown by means of chemical vapor deposition (CVD). This process leads to transferred graphene layers free of polymer contamination. The absence of polymer residues boosts the surface-enhanced Raman scattering (SERS) of the CVD graphene with gold nanoparticles (Au NPs) deposited atop by evaporation. The SERS enhancement of the CVD graphene reaches similar to 120 for the characteristic 2D peak of graphene, the highest enhancement factor achieved to date, when the Au NPs are at the threshold of percolation. Our simulation supported by experiment suggests that the polymer residues persistently present on the graphene transferred by the conventional polymer-assisted method are equivalent to an ultrathin film of less than 1 nm thickness. The presence of polymer residues drastically reduces SERS due to the separation of the Au NPs from the underlying graphene. The scalability of CVD graphene opens up for the possibility of graphene-based SERS sensors.

    Nationell ämneskategori
    Fysik Teknik och teknologier
    Identifikatorer
    urn:nbn:se:uu:diva-269192 (URN)10.1016/j.carbon.2015.11.043 (DOI)000367233000070 ()
    Forskningsfinansiär
    Knut och Alice Wallenbergs Stiftelse, 2011.0113Knut och Alice Wallenbergs Stiftelse, 2011.0082Stiftelsen för strategisk forskning (SSF), SE13-0061Vetenskapsrådet, 621-2014-5591
    Tillgänglig från: 2015-12-14 Skapad: 2015-12-14 Senast uppdaterad: 2017-12-01Bibliografiskt granskad
  • 79.
    Ahlberg, Patrik
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Hinnemo, Malkolm
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Song, Man
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Gao, Xindong
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Olsson, Jörgen
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Zhang, Shi-Li
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.
    Zhang, Zhi-Bin
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Fasta tillståndets elektronik.