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  • 1.
    Balliu, Enkeleda
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Nilsson, Hans-Erik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    A compact, single-frequency, high-power, SBS-free, Yb-doped single-stage fiber amplifier2019Inngår i: Proceedings of SPIE - The International Society for Optical Engineering / [ed] W. Andrew Clarkson and Ramesh K. Shori, SPIE - International Society for Optical Engineering, 2019, Vol. 10896, s. 6pp-, artikkel-id 1089618Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Interest in compact, single-frequency fiber amplifier has increased within many scientific and industrial applications. The main challenge is the onset of nonlinear effects, which limit their power scaling. Here we demonstrate a compact, high-power, single-frequency, polarization-maintaining, continous-wave fiber amplifier using only one amplification stage. We developed the fiber amplifier using a master oscillator fiber amplifier architecture, where a low-noise, single-frequency, solid-state laser operating at 1064 nm was used as a seed source. We evaluated the amplifier's performance by using several state-of-the-art, small-core, Ytterbium (yb)-doped fibers, as well as an in-house-made, highly Yb-doped fiber. An output power of 82 W was achieved with no sign of stimulated Brillouin scattering. A good beam quality and a polarization extinction ratio (PER) of > 25 dB were achieved. The compact fiber amplifier can be a competitive alternative to multi stage designed fiber amplifiers.

  • 2.
    Balliu, Enkeleda
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Thontakudi, Anjali
    Monta Vista High School, Cupertino, CA USA.
    Knall, Jenny M.
    Stanford University, Stanford, CA USA.
    Digonnet, Michel J. F.
    Stanford University, Stanford, CA USA.
    Predictive comparison of anti-Stokes fluorescence cooling in oxide and non-oxide fiber hosts doped with Er3+, Pr3+, or Yb3+2019Inngår i: Proceedings of SPIE - The International Society for Optical Engineering: Photonic Heat Engines: Science and Applications, SPIE - International Society for Optical Engineering, 2019, Vol. 10936, artikkel-id 109360JKonferansepaper (Fagfellevurdert)
    Abstract [en]

    A comprehensive study was performed to quantify anti-Stokes-fluorescence (ASF) cooling in fibers of various host compositions (telluride, fluorozirconates, fluorophosphates, phosphates, and chalcogenides) doped with Yb3+ or Er3+. Published expressions were used to calculate the maximum heat that can be extracted per unit length and time from a single-mode fiber in the limit of negligible absorptive loss, and the associated cooling efficiency. These expressions consider host- and ion-dependent parameters, namely the absorption and emission cross-section spectra, the radiative and nonradiative lifetimes, and the critical concentration for quenching. Using these expressions with published values for these parameters, the maximum extractable heat was calculated for a large-mode-area fiber (NA = 0.05) doped with either Yb3+ or Er3+ in a variety of hosts. The results show that for a given ion, the maximum heat that can be extracted depends strongly on the host due to the strong dependence of quenching on host composition. In contrast, the cooling efficiency (ratio of extracted heat to pump power absorbed) depends very weakly on the host. The cooling efficiency is also almost twice as high for Er3+ (average of 3.8%) than for Yb3+ (average of 2.2%) due to the larger gap between the pump and mean fluorescence energy in Er3+. Of the limited number of materials for which a full set of data was found in the literature, the highest extractable heat for Yb3+ is in phosphate (-51.5 mW/m), and for Er3+ is in chalcogenide (-10.3 mW/m). This work provides a simple methodology to evaluate the quantitative cooling performance of these and other rare-earth ions in any amorphous host, a procedure that should guide researchers in the selection of optimum materials for ASF cooling of fibers.

  • 3.
    Blomquist, Nicklas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Large-Scale Graphene Production for Environmentally Friendly and Low-Cost Energy Storage: Production, Coating, and Applications2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    There is great demand for energy-efficient, environmentally sustainable, and cost-effective electrical energy storage devices. One important aspect of this demand is the need for automotive electrification to achieve more energy-efficient transportation at a reasonable cost, thus supporting a fossil-fuel free society. Another important aspect is the requirement for energy storage in the growing field of renewable energy production from wind and solar sources, which generates an irregular supply of electricity due to weather conditions.Much of the research in this area has been conducted in the field of battery technology with impressive results, but the need for rapid storage devices such as supercapacitors is growing. Due to the excellent ability of supercapacitors to handle short peak power pulses with high efficiency along with their long lifetime and superior cyclability, their implementations range from small consumer electronics to electric vehicles and stationary grid applications. Supercapacitors also have the potential to complement batteries to improve pulse efficiency and lifetime of the system, however, the cost of supercapacitors is a significant issue for large-scale commercial use, leading to a demand for sustainable, low-cost materials and simplified manufacturing processes. An important way to address this need is to develop a cost-efficient and environment-friendly large-scale process to produce highly conductive nanographites, such as graphene and graphite nanoplatelets, along with methods to manufacture low-cost electrodes from large area coating.

    In this thesis, I present a novel process to mechanically exfoliate industrial quantities of nanographite from graphite in an aqueous environment with low energy consumption and at controlled shear conditions. The process is based on hydrodynamic tube-shearing and can produce both multilayer graphene and nanometer-thick and micrometer-wide flakes of nanographite. I also describe the production of highly conductive and robust carbon composites based on the addition of nanocellulose during production; these are suitable as electrodes in applications ranging from supercapacitors and batteries to printed electronics and solar cells.Furthermore I demonstrate a scalable route for roll-to-roll coating of the nanographite-nanocellulose electrode material and propose a novel aqueous, low-cost, and metal-free supercapacitor concept with graphite foil functioning as the current collector. The supercapacitors possessedmore than half the specific capacitance of commercial units but achieved a material cost reduction of more than 90 %, demonstrating anenvironment-friendly, low-cost alternative to conventional supercapacitors.

  • 4.
    Blomquist, Nicklas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Paper based Supercapacitors for vehicle KERS-application2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    High mobility has been a standard in the modern world for decades. This has resulted in high energy consumption, diminishing fossil energy reserves and rising levels of greenhouse gases.

    By recovering the energy lost in deceleration of vehicles the total energy consumption can be decreased and exhaust emissions reduced. This can be done with a kinetic energy recovery system (KERS) that converts kinetic energy to electric energy during deceleration, which then can be used for acceleration.

    KERS requires an electrical storage device with high power density, due to the high power levels generated at heavy braking. Batteries does not generally meet these requirements, especially in the cost-effective point of view, but different types of capacitors can be used to obtain a cheap and effective system. To get such an energy storage device small, lightweight and inexpensive while the technology is sustainable requires avoidance of rare metals and hazardous materials.

    In this master thesis energy and power levels for KERS has been modelled, based on standardized measurements techniques and small paper-based supercapacitors have been built and tested in order to model size, weight and price for a full-scale energy storage device to a KERS-application.

    The models showed that energy consumption in urban traffic could be reduced with 18% and with an electrode material for the energy storage device with a capacitance of about 1500 F/m2 a reasonable size and weight is obtained. To reach these values of capacitance in paper-based supercapacitors further testing is required on area and layer dependence and for different electrodes.

  • 5.
    Edvardsson, Sverker
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Gradin, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Isaksson, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    On dissipative effects of paper web adhesion strength2011Inngår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 48, nr 1, s. 24-30Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work is concerned with the adhesion strength between a paper web and a metal roll surface, which is a common situation in paper machines world-wide. It is shown that the classic expression relating the work of adhesion to the peeling angle and web tension is, in general, insufficient. An improved model is suggested to take into account the energy dissipation due to elastic-plastic deformation behavior of wet paper materials. To judge the model, an industrially relevant example of wet newsprint and a mild steel surface is studied. It is found that the agreement between theory and experimental observations is excellent. A key result is that elastic-plastic material behavior must always be included for wet paper materials in peeling processes.

  • 6.
    Edvardsson, Sverker
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Gulliksson, Mårten
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Persson, Johan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    The dynamical functional particle method: an approach for boundary value problems2012Inngår i: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 79, nr 2, s. art. no. 021012-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present work is concerned with new ideas of potential value for solving differential equations. First, a brief introduction to particle methods in mechanics is made by revisiting the vibrating string. The full case of nonlinear motion is studied and the corresponding nonlinear differential equations are derived. It is suggested that the particle origin of these equations is of more general interest than usually considered. A novel possibility to develop particle methods for solving differential equations in a direct way is investigated. The dynamical functional particle method (DFPM) is developed as a solution method for boundary value problems. DFPM is based on the concept of an interaction functional as a dynamical force field acting on quasi particles. The approach is not limited to linear equations. We exemplify by applying DFPM to several linear Schrödinger type of problems as well as a nonlinear case. It is seen that DFPM performs very well in comparison with some standard numerical libraries. In all cases, the convergence rates are exponential in time. © 2012 American Society of Mechanical Engineers.

  • 7.
    Edvardsson, Sverker
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Neuman, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Edström, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Gulliksson, Mårten
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Role of the particle method DFPM for solving linear equationsManuskript (preprint) (Annet vitenskapelig)
  • 8.
    Gustafsson Coppel, Ludovic
    et al.
    Gjovik Univ Coll, Fac Comp Sci & Media Technol, N-2815 Gjovik, Norway.
    Johansson, Niklas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Neuman, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Angular dependence of fluorescence from turbid media2015Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, nr 15, s. 19552-19564Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We perform Monte Carlo light scattering simulations to study the angular distribution of the fluorescence emission from turbid media and compare the results to measured angular distributions from fluorescing white paper samples. The angular distribution of fluorescence emission is significantly depending on the concentration of fluorophores. The simulations show also a dependence on the angle of incidence that is however not as evident in the measurements. A detailed analysis of the factors affecting this angular distribution indicates that it is strongly correlated to the mean depth of the fluorescence process. The findings can find applications in fluorescence spectroscopy and are of particular interest when optimizing the impact of fluorescence on e.g.the appearance of paper as the measured values are angle dependent.

  • 9.
    Gustafsson Coppel, Ludovic
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Neuman, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Edström, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Lateral light scattering in paper - MTF simulation and measurement2011Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 19, nr 25, s. 25181-25187Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The modulation transfer function (MTF) of 22 paper samples is computed using Monte Carlo simulations with isotropic or strongly forward single scattering. The inverse frequency at half maximum of the MTF (kp) is found inappropriate as a single metric for the MTF since it is insensitive to the shape of the modeled and simulated MTF. The single scattering phase function has a significant impact on the shape of the MTF, leading to more lateral scattering. However, anisotropic single scattering cannot explain the larger lateral scattering observed in paper. It is argued that the directional inhomogeneity of paper requires a light scattering model with both the phase function and scattering distances being dependent on the absolute direction.

  • 10.
    Hammarling, Krister
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Engholm, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Muri, Harald Ian
    NTNU, Trondheim, Norway.
    Wahl, Markus Solberg
    NTNU, Trondheim, Norway.
    Hjelme, Dag Roar
    NTNU, Trondheim, Norway.
    Dual parameter fiber optic sensor combining a Fabry-Perot and a Mach-Zehnder interferometer2017Inngår i: Proceedings of IEEE Sensors, IEEE, 2017, s. 1440-1442Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    A new concept for dual parameter fiber optic sensorhas been developed and characterized, both in a two-fiber andsingle-fiber configuration. The liquid sensor measures ethanolconcentration with a stimuli responsive hydrogel whichconstitutes a low finesse Fabry-Perot cavity, and refractive indexwith a Mach-Zehnder type fiber optic interferometer. The two-fiber configuration utilize a fiber optic 1310/1550 nm wavelengthdivision multiplexer to separate the two parameters, while aversatile filtering algorithm extracts and separates the twoparameters in the single-fiber configuration. No cross talk wereobserved for the measured parameters of free spectral range andrefractive index for the two-fiber configurations, while for thesingle fiber configuration cross-talk were observed. The twoconfigurations prove to be versatile dual parametric fiber opticsensor concepts for accurate detection of specific parameters,based on stimuli responsive hydrogels.

  • 11.
    Johansson, Niklas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Measuring and modelling light scattering in paper2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [sv]

    Avhandlingen behandlar de teoretiska och praktiska aspekterna av att använda spektrala vinkelupplösta reflektansmätningar för optisk karakterisering av fiberbaserade material såsom papper och kartong. En spektral goniofotometer används för att mäta det reflekterade ljusets vinkelfördelning. En stor del av arbetet utgörs av att utvärdera instrumentets noggrannhet, samt utreda hur de vinkelupplösta mätningarna skall utföras på bästa sätt för att erhålla en så fullständig karakterisering som möjligt. Det reflekterade ljuset består av tre komponenter; ytreflektans, bulkreflektans samt fluorescens. En fullständig karakterisering förutsätter att dessa tre komponenter kan analyseras separat, vilket i detta arbete görs genom nyutvecklade metoder.

    En metod har utvecklats för separation av ytreflektans och bulkreflektans. Metoden bygger på att analysera hur den totala reflektansen förändras vid ökande absorption i det reflekterande materialet. Absorptionen kontrolleras genom inkjet-tryckning där tryckfärg appliceras på substratet i sådan mängd att bulkreflektansen helt släcks ut. Genom att kombinera mätningar på tryckt och otryckt substrat kan de båda komponenterna separeras. Trots att ytreflektansen från ett matt papper är liten i förhållande till bulkreflektansen, så visar resultaten att den ökar markant med ökande betraktningsvinkel och kan därmed ha stor inverkan på den totala reflektansen. Bidraget från fluorescens kan kvantitativt analyseras genom att kombinera mätningar utförda med respektive utan UV-filter. Vinkelupplösta mätningar och Monte Carlo-simuleringar av fluorescensens vinkelfördelning visar att dess anisotropi är relaterad till det medeldjup vid vilket fluorescensen emitteras. Resultaten förklarar observerade skillnader och motstridigheter i tidigare rapporterade studier kring huruvida fluorescens kan anses vara Lamberskt fördelad.

    Samtliga goniofotometriska mätningar är utförda med ett kompakt, kommersiellt tillgängligt, dubbelstråleinstrument. För att undersöka instrumentets lämplighet för absoluta reflektansmätningar utförs en analys av dess mätnoggrannhet. Resultaten visar att instrumentets kompakta storlek i kombination med den anisotropa reflektansen från papper introducerar systematiska fel av samma storleksordning som den totala mätnoggrannheten. Dessa fel uppstår på grund av den relativt stora detektorapertur som måste användas vid mätningar av diffus reflektans, vilket är karakteristiskt för papper och kartong. Resultaten visar även att felen är störst vid flacka mätvinklar och för prover med hög grad av anisotropisk reflektans, och en geometrisk korrektionsmetod för denna typ av systematiska fel föreslås.

    Spektrala och vinkelupplösta mätningar medför per automatik stora mängder mätdata. Genom att använda strålningstransportteori som en matematisk modell för hur ljus sprids i papper kan mätdatat reduceras till en uppsättning beskrivande materialparameterar. Att uppskatta dessa optiska parametrar utifrån vinkelupplösta reflektansmätningar är i sig ett komplicerat problem, vilket dessutom är känsligt för mätfel och val av mätvinklar. Detta inversa problem analyseras i detalj, och speciellt hur valet av mätvinklar kan reduceras utan att försämra förutsättningarna för estimeringen. Simuleringar visar att mätningarna kan begränsas till infallsplanet, eller till och med enbart framåtriktningen, så länge tillräckligt flacka mätvinklar är inkluderade i mätsekvensen.

  • 12.
    Johansson, Niklas
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Andersson, Mattias
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Angular variations of reflectance and fluorescence from paper - the influence of fluorescent whitening agents and fillers2012Inngår i: Final Program and Proceedings - IS and T/SID Color Imaging Conference, Springfield, USA: The Society for Imaging Science and Technology, 2012, s. 236-241Konferansepaper (Fagfellevurdert)
    Abstract [en]

    It has earlier been shown that light reflected from the bodyof paper exhibit anisotropic behavior. On the other hand, fluores-cence emission is often assumed to be distributed in a Lambertianmanner. The angular behavior of light reflected and fluorescedfrom paper is examined using measurements from a spectral go-niophotometer. The angular dependency of the radiance factorswas measured for a range of excitation wavelengths. Moreover,the influence of fillers and fluorescent whitening agents (FWA)on the anisotropy was studied. The measurements show that theanisotropy of the total radiance factor of paper decreases whenan increasing amount of FWA is added to the paper. The sameeffect was also observed when an increased amount of filler wasadded to the paper. In addition, it was shown that the presenceof fillers reduce the effect of the FWA. The results show that incomparison to the anisotropy of the total radiance factor from thepaper samples, the anisotropy of the fluorescence alone is negligi-ble. Hence, for paper samples containing FWA evenly distributedin the bulk, the fluorescence alone should not induce significantdifferences between color measuring instruments of different mea-surement geometries.

  • 13.
    Johansson, Niklas
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Neuman, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Andersson, Mattias
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Edström, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Separation of surface and bulk reflectance by absorption of bulk scattered light2013Inngår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 52, nr 19, s. 4749-4754Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A method is proposed for separating light reflected from turbid media with a rough surface into a bulkand a surface component. Dye is added to the sample, thereby increasing absorption and canceling bulkscattering. The remaining reflected light is surface reflectance, which can be subtracted from the totalreflectance of an undyed sample to obtain the bulk component. The method is applied to paper wherethe addition of dye is accomplished by inkjet printing. The results show that the bulk scattered light isefficiently canceled, and that both the spectrally neutral surface reflectance and the surface topographyof the undyed paper is maintained. The proposed method is particularly suitable for characterization ofdielectric, highly randomized materials with significant bulk reflectance and rough surfaces, which aredifficult to analyze with existing methods. A reliable separation method opens up for new ways of analyzing,e.g., biological tissues and optical coatings, and is also a valuable tool in the development of morecomprehensive reflectance models.

  • 14.
    Johansson, Niklas
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Neuman, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Andersson, Mattias
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Edström, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    The inverse radiative transfer problem - considerations for optically thick mediaArtikkel i tidsskrift (Fagfellevurdert)
  • 15.
    Linder, Tomas
    et al.
    Department of Computer Science, Electrical and Space Engineering Luleå University of Technology.
    Löfqvist, Torbjörn
    Department of Computer Science, Electrical and Space Engineering Luleå University of Technology.
    Gustafsson Coppel, Ludovic
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Neuman, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Edström, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Lateral light scattering in fibrous media2013Inngår i: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, nr 6, s. 7835-7840Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Lateral light scattering in fibrous media is investigated by computing the modulation transfer function (MTF) of 22 paper samples using a Monte Carlo model. The simulation tool uses phase functions from infinitely long homogenous cylinders and the directional inhomogeneity of paper is achieved by aligning the cylinders in the plane. The inverse frequency at half maximum of the MTF is compared to both measurements and previous simulations with isotropic and strongly forward single scattering phase functions. It is found that the conical scattering by cylinders enhances the lateral scattering and therefore predicts a larger extent of lateral light scattering than models using rotationally invariant single scattering phase functions. However, it does not fully reach the levels of lateral scattering observed in measurements. It is argued that the hollow lumen of a wood fiber or dependent scattering effects must be considered for a complete description of lateral light scattering in paper.

  • 16.
    Lundberg, Anna
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Ink-paper interactions and effect on print quality in inkjet printing2011Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis concerns paper and ink interactions related to inkjet printing. The

    main purpose of this work was to gain a deeper understanding in which

    parameters control the flow of ink into papers and how the ink interacts with the

    paper surface. The overall objective was to find key parameters to optimize the

    print quality in inkjet printing. Characterization of paper-surfaces in terms of porosity, surface roughness and

    surface energy was made. Objective and subjective measurements were used for

    print quality evaluation. Light microscopy imaging and SEM was used to see how

    ink interacts with the paper surface in a printed image. A high speed camera was

    used to study the absorption of picolitre sized inkjet droplets into fine papers.

    An initial study on the effect of paper properties on print quality was made.

    Result indicated that there were small differences in print quality for pilot papers

    with different composition (in a specific parameter window) and the commercial

    paper COLORLOK® reproduced a noticeable high colour gamut compared to the

    other samples.Research was made to see how surface fixation can affect the print quality for

    printouts made with pigmented ink. Surface fixation promotes retention of the

    pigmented colorant in the outermost surface layer of the paper and has been

    denoted “colorant fixation” in this thesis.

    It was shown that applying colorant fixation onto a paper surface before

    printing can increase the detail reproduction in a printed image. Different

    concentrations of calcium chloride were applied onto the paper surface on fullscale

    produced non-commercial papers. Test printing was made with a SoHo

    (Small office/Home office) printer using pigmented ink and results showed that

    using calcium chloride as surface treatment can lead to aggregation of pigments at

    the surface resulting in a higher detail reproduction.

    Fast absorption of the carrier liquid into the paper and fast fixation of

    colourants on the surface is important in inkjet printing to avoid colour to colour

    bleeding. These demands will be more pronounced when the printing speed

    increases. It is important to understand which parameters affect the absorption process to

    be able to control the mechanisms and to optimize the print quality.

    A study of absorption of picolitre size inkjet droplets into fine paper was made

    in this work. Theoretical equations describing fluid absorption into capillaries were

    tested and compared with experimental results. The result showed that the time

    dependence in the Lucas-Washburn (L-W) equation fits fairly well to data whereas

    the L-W equation overestimates the penetration depth.

    The results are directly applicable to paper and printing industry and can be

    used as a base for future studies of absorption of picolitre sized droplets into

    porous materials and for studies of aggregation of colloidal particles on surfaces.

  • 17.
    Neuman, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Applied problems and computational methods in radiative transfer2013Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Light scattering in turbid media is essential for such diverse applications as paperand print, computer rendering, optical tomography, astrophysics and remote sensing.This thesis investigates angular variations of light reflected from plane-parallelturbid media using both mathematical models and reflectance measurements, dealswith several applications and proposes novel computational methods for solving thegoverning equations.Angular variations of light reflected from plane-parallel turbid media is studiedusing both mathematical models and reflectance measurements. It is found that thelight is reflected anisotropically from all media encountered in practice, and that theangular variations depend on the medium absorption and transmittance and on theangular distribution of the incident light. If near-surface bulk scattering dominates,as in strongly absorbing or highly transmitting media or obliquely illuminated media,relatively more light is reflected in large polar (grazing) angles. These results areconfirmed by measurements using a set of paper samples. The only situation withisotropic reflectance is when a non-transmitting, non-absorbing medium is illuminateddiffusely, and it is shown that this is the only situation where the widely usedKubelka-Munk model is exactly valid.A number of applied problems is studied, including reflectance measurements,angle resolved color and point spreading. It is seen that differences in instrumentdetection and illumination geometry can result in measurement differences. The differencesare small and if other sources of error — such as fluorescence and gloss— are not eliminated, the differences related to instrument geometry become difficultto discern. Furthermore, the dependence of point spreading in turbid mediaon the medium parameters is studied. The asymmetry factor is varied while maintainingconstant the optical response in a standardized measurement geometry. It isseen that the point spreading increases as forward scattering becomes more dominant,and that the effect is larger if the medium is low-absorbing with large meanfree path. It is argued that the directional inhomogeneity of the scattering mediummust be captured by the model to reproduce experimental results. Finally, the angleresolved color of a set of paper samples is assessed both theoretically and experimentally.The chroma decreases and the lightness increases as the observation polarangle increases. The observed differences are clearly large, and a modification ofthe L∗a∗b∗ formalism including angle dependent chromatic adaptation is suggestedhere to handle this situation.

    The long standing issue of parameter dependence in the Kubelka-Munk modelis partially explained by recognizing that light reflected from paper samples in standardizedmeasurements has angular variations, and by using the appropriatemodelin the calculation of the scattering and absorption coefficients.The radiative transfer (RT) equation is solved with a recently proposed particlemethod (DFPM), both in standard cases and in cases previously considered intractable.Fluorescence is added to the RT equation, thus including wavelength asan additional dimension, and this equation is solved using DFPM. The discrete RTequation can be written as a system of linear equations, and a comprehensive analysisof the convergence properties of DFPM when solving this type of problems ispresented.

  • 18.
    Neuman, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Edvardsson, Sverker
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Edström, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    A particle approach to the radiative transfer equation with fluorescence2013Artikkel i tidsskrift (Fagfellevurdert)
  • 19.
    Neuman, Magnus
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    G. Coppel, Ludovic
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Edström, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Angle resolved color of bulk scattering media2011Inngår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, nr 36, s. 6555-6563Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The angle resolved reflectance factor of matte samples is measured with a goniophotometer and simulated using radiative transfer theory. Both measurements and simulations display the same characteristic dependence of the reflectance factor on the observation angle. The angle resolved reflectance spectra are translated to CIELAB color coordinates and the angular color differences are found to be surprisingly large. A chromatic adaptation that is dependent on the observation angle is suggested, in which a nonabsorbing opaque medium is used as the reference white, and the angular color differences are then reduced. Furthermore, the use of an undyed paper as the reference white is evaluated. The angular lightness differences are then reduced further, but the angular differences in chroma are still large. It is suggested that smaller variations in perceived color could be explained by angle dependent chromatic adaptation and a limited sensitivity of the human visual system to changes in chroma.

  • 20.
    Singh, S.
    et al.
    Institute of Physics of the ASCR, ELI-Beamlines, Czech Republic.
    Slavicek, Tomas
    Czech Technical University in Prague, Prague, Czech Republic.
    Hodak, R.
    Czech Technical University in Prague, Prague, Czech Republic.
    Versaci, R.
    Institute of Physics of the ASCR, ELI-Beamlines, Czech Republic.
    Pridal, P.
    Czech Technical University in Prague, Prague, Czech Republic.
    Kumar, D.
    Institute of Physics of the ASCR, ELI-Beamlines, Czech Republic.
    Absolute calibration of imaging plate detectors for electron kinetic energies between 150 keV and 1.75 MeV2017Inngår i: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 88, nr 7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the calibration of two different kinds of image plates (IPs) for detecting electrons with kinetic energy in the range of 150 keV-1.75 MeV. The calibration was performed using a Sr-90 beta source. The paper also provides the measured fading response for the IPs in the time range from 12 min to 18 h. Calibration results are compared to Monte Carlo simulations of energy deposited by the electrons in the sensitive layer of the IPs. It was found that within this energy range a linear relation between simulated energy deposited by the electron in the phosphor layer and the measured photo stimulated luminescence in the IP is adequate to model the response of the IP. 

  • 21.
    Slavicek, Tomas
    et al.
    Institute of Experimental and Applied Physics, Czech Technical University in Prague, Horska 3a/22, 128 00 Praha, Czech Republic.
    Kralik, M
    Czech Metrology Institute, Radiová 1, 102 00 Praha 10, Czech Republic.
    Krapohl, David
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Petersson, Sture
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    Pospisil, S
    Institute of Experimental and Applied Physics, Czech Technical University in Prague, Horska 3a/22, 128 00 Praha, Czech Republic.
    Thungström, Göran
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för informationsteknologi och medier.
    A thermal neutron detector based on planar silicon sensor with TiB 2 coating2012Inngår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 7, nr 1, s. Art. no. C01053-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Neutron radiation as a non-ionizing radiation is particularly difficult to detect; therefore a conversion material is required. The conversion material converts neutrons into secondary charged particles in order for them to be detected in a silicon detector. The use of titanium diboride (TiB 2) as the conversion material deposited by an electron beam-physical vapour deposition (EB-PVD) as a part of a front-side contact of a planar silicon detector is presented. The effect of different front-side contact material compositions is discussed. The detectors behaviour was examined using alpha particles and thermal neutrons from an 241Am-Be source. Simultaneously, a Geant4 simulation was so as executed to evaluate the conversion layer functionality and to discover the conversion material thickness for the best neutron detection efficiency. © 2012 IOP Publishing Ltd and SISSA.

  • 22. Slavicek, Tomas
    et al.
    Pospisil, S.
    Advanced Detectors for Better Awareness of Neutrons and Gamma Rays in Environment2017Rapport (Annet vitenskapelig)
  • 23. Slavicek, Tomas
    et al.
    Pospisil, S.
    Masek, P.
    Urban, T.
    Trojek, T.
    Kohout, Z.
    Development of Neutron Image Sensor Technology for AD-BANG project2016Inngår i: 2016 IEEE NSS/MIC, 2016Konferansepaper (Fagfellevurdert)
  • 24.
    Slavicek, Tomas
    et al.
    Czech Technical University in Prague, Czech Republic .
    Pospisil, Stanislav
    Advanced Detectors for Better Awareness of Neutrons and Gamma Rays in Environment2016Rapport (Annet vitenskapelig)
  • 25.
    Uesaka, Tetsu
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för tillämpad naturvetenskap och design.
    Fibre-fibre bond: What paper physicist sees2012Konferansepaper (Annet vitenskapelig)
  • 26.
    Ulyanov, A.
    et al.
    School of Physics, University College Dublin, Ireland.
    Morris, O.
    School of Physics, University College Dublin, Ireland; Galway-Mayo Institute of Technology, Galway, Ireland.
    Hanlon, L
    School of Physics, University College Dublin, Ireland.
    Mc Breen, S
    School of Physics, University College Dublin, Ireland.
    Foley, S
    School of Physics, University College Dublin, Ireland.
    Roberts, O
    School of Physics, University College Dublin, Ireland.
    Tobin, I
    School of Physics, University College Dublin, Ireland.
    Murphy, D
    School of Physics, University College Dublin, Ireland.
    Wade, C
    School of Physics, University College Dublin, Ireland.
    Nelms, N
    European Space Agency, ESTEC.
    Shortt, B
    European Space Agency, ESTEC.
    Slavicek, Tomas
    Czech Technical University in Prague.
    Granja, C.
    Czech Technical University in Prague.
    Solar, M.
    Czech Technical University in Prague.
    Performance of a monolithic LaBr3: Ce crystal coupled to an array of silicon photomultipliers2016Inngår i: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 810, nr 810, s. 107-119Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A gamma-ray detector composed of a single 28×28×20 mm3 LaBr3:Ce crystal coupled to a custom built 4×4 array of silicon photomultipliers was tested over an energy range of 30 keV to 9.3 MeV. The silicon photomultipliers were initially calibrated using 20 ns light pulses generated by a light emitting diode. The photodetector responses measured as a function of the number of incident photons were found to be non-linear and consistent with model predictions. Using corrections for the non-linearity of the silicon photomultipliers, the detector showed a linear response to gamma-rays with energies from 100 keV to the maximum available energy of 9.3 MeV. The energy resolution was found to be 4% FWHM at 662 keV. Despite the large thickness of the scintillator (20 mm) and a 5 mm thick optical window, the detector was capable of measuring the positions of the gamma-ray interaction points. The position resolution was measured at 356 keV and was found to be 8 mm FWHM in the detector plane and 11 mm FWHM for the depth of interaction. The detector can be used as a building block of a larger calorimeter system that is capable of measuring gamma-ray energies up to tens of MeV.

  • 27. Urban, T.
    et al.
    Slavicek, Tomas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Hulka, J.
    Kok, A.
    Meier, D.
    Masek, P.
    Pospisil, S.
    Koybasi, O.
    Trojek, T.
    Stripové křemíkové senzory pro měření ve směsných neutron-gama radiačních polích2016Inngår i: XXXVIII. Dny radiačni ochrany, 2016Konferansepaper (Annet vitenskapelig)
  • 28. Urban, T.
    et al.
    Slavicek, Tomas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Pospisil, S.
    Kok, A.
    Trojek, T.
    New Neutron Detector Design Optimization by Monte Carlo Simulation2016Konferansepaper (Fagfellevurdert)
  • 29.
    Zhang, Renyun
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Hummelgård, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Örtegren, Jonas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Olsen, Martin
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Interaction of the human body with triboelectric nanogenerators2019Inngår i: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 57, s. 279-292Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The use of triboelectric nanogenerators (TENGs) is a new technique for energy harvesting at both small and large scales. Almost all types of mechanical energy can be harvested with TENGs by using four modes of operation that cover almost all mechanical motions. The interactions of the human body with TENGs range from energy harvesting, motion sensing, and biomedical applications to human-computer communications. Different types of TENGs have been developed to directly or indirectly involve the human body. This review will summarize the recent advances in the interaction of the human body with TENGs.

  • 30.
    Zhang, Renyun
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Hummelgård, Magnus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Örtegren, Jonas
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Olsen, Martin
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Andersson, Henrik
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för elektronikkonstruktion.
    Yang, Ya
    CAS Center for Excellence in Nanoscience, Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, Beijing 100083, P. R. China.
    Olin, Håkan
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Human body constituted triboelectric nanogenerators as energy harvesters, code transmitters and motion sensors2018Inngår i: ACS Applied Energy Materials, ISSN 2574-0962, Vol. 1, nr 6, s. 2955-2960Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Human skin is a dielectric material that can be used as a triboelectric material for harvesting energy from body motions. The output power of such a human skin-based triboelectric nanogenerator (TENG) is relatively low. Here, we assembled high-output human body constituted TENGs (H-TENGs) by taking advantage of the unique electrical properties of the human body, such as high skin impedance, low tissue resistance, body capacitance, and conductivity. The output of a H-TENG can reach 30 W/m2, which is enough to drive small electronic devices, such as a timer or a calculator. The unique feature of the H-TENG is that it can perform the four fundamental modes of TENGs, which has not been reported elsewhere. Such a feature allows the H-TENG to act as a code transmitter to send light and electrical signals, such as Morse code. H-TENGs also benefit the development of high-performance, self-powered body motion sensors. Our findings suggest new strategies for harvesting energy from human body motions, as well as new types of motion sensors and signal senders.

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