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  • 1.
    Ali, S.
    et al.
    Univ Stockholm, Dept Phys, S-10691 Stockholm, Sweden.
    Orban, I.
    Univ Stockholm, Dept Phys, S-10691 Stockholm, Sweden.
    Mahmood, S.
    Univ Stockholm, Dept Phys, S-10691 Stockholm, Sweden.
    Altun, Z.
    Marmara Univ, Dept Phys, TR-81040 Istanbul, Turkey.
    Glans, Peter
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Schuch, R.
    Univ Stockholm, Dept Phys, S-10691 Stockholm, Sweden.
    ELECTRON-ION RECOMBINATION RATE COEFFICIENTS FOR C II FORMING C I2012In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 753, no 2, p. Art. no. 132-Article in journal (Refereed)
    Abstract [en]

    We have determined absolute dielectronic recombination rate coefficients for C II, using the CRYRING heavy-ions storage ring. The resonances due to 2s-2p (Delta n= 0) core excitations are detected in the center-of-mass energy range of 0-15 eV. The experimental results are compared with intermediate coupling AUTOSTRUCTURE calculations. Plasma rate coefficients are obtained from the DR spectrum by convoluting it with a Maxwell-Boltzmann energy distribution for temperatures in the range of 10(3)-10(6) K. The derived temperature-dependent plasma recombination rate coefficients are presented graphically and parameterized by using a fit formula for convenient use in plasma modeling codes. The experimental rate coefficients are also compared with the theoretical data available in literature. In the temperature range of 10(3)-2 x 10(4) K, our experimental results show that previous calculations severely underestimate the plasma rate coefficients and also our AUTOSTRUCTURE calculation does not reproduce the experimental plasma rate coefficients well. Above 2x10(4) K, the agreement between the experimental and theoretical rate coefficients is much better, and the deviations are smaller than the estimated uncertainties.

  • 2.
    Ashraf, Shakeel
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Niskanen, Ilpo
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. University of Oulu, Finland.
    Kanyathare, Boniphace
    Electronics and Telecommunications Department, Dar es salaam Institute of Technology, Tanzania.
    Vartiainen, Erik
    LUT School of Engineering Science, Lappeenranta University of Technology, Finland.
    Mattsson, Claes
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Heikkilä, Rauno
    Faculty of Technology, Structures and Construction Technology, University of Oulu, Finland.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Determination of complex refractive index of SU-8 by Kramers-Kronig dispersion relation method at the wavelength range 2.5 – 22.0 μm2019In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 224, p. 309-311Article in journal (Refereed)
    Abstract [en]

    Accurate determination of the complex refractive index of SU-8 epoxy has significant for the wide variety of applications in optical sensor technology at IR range. The complex refractive index of SU-8 is determined by recording the transmission of light spectra for the wavelength range of 2.5 – 22.0 μm.  The data analysis is based on the Kramers-Kronig dispersion relation method. The method has several merits, such as ease of operation, non-contact technique, measurement accuracy, and rapid measurement. The present method is not restricted to the case of SU-8 but it is also proposed to be applicable across a broad range of applications, such as assessment of the optical properties of paints and biomedical samples.

  • 3.
    Engholm, Magnus
    et al.
    Fiber Optic Valley AB.
    Jelger, P.
    KTH.
    Laurell, F.
    KTH.
    Norin, L.
    Acreo FiberLab.
    Improved photodarkening resistivity in ytterbium-doped fiber lasers by cerium codoping2009In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 34, no 8, p. 1285-1287Article in journal (Refereed)
    Abstract [en]

    We show that the photodarkening resistivity of ytterbium-doped fiber lasers can be greatly improved by cerium codoping. It is suggested that the coexistence of the redox couple Ce3+⁄Ce4+ in the glass provides means for trapping both hole- and electron-related color centers that are responsible for the induced optical losses in Yb-doped fiber lasers.

  • 4. Engholm, Magnus
    et al.
    Norin, Lars
    Acreo FiberLab AB.
    The role of charge transfer processes for the induced optical lossesin ytterbium doped fiber lasers2009In: The role of charge transfer processes for the induced optical lossesin ytterbium doped fiber lasers, 2009, Vol. 7195, no 71950TConference paper (Refereed)
    Abstract [en]

    In this paper we present how charge transfer processes influences the induced optical losses (photodarkening) in ytterbium doped fiber lasers. The location of the charge transfer absorption band is strongly composition dependent and is correlated to the valence stability of the ytterbium ion in the silicate glass matrix. An improved photodarkening performance can in general be observed for a charge-transfer band shifted to shorter wavelengths, although other routes are also possible to reduce photodarkening. Other parameters that affect the laser performance, such as absorption and emission cross section, must also be considered.

  • 5.
    Forsberg, Viviane
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Hummelgård, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Zhang, Renyun
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Olin, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Cellulose stabilizers for 2D materials inkjet inks2017Conference paper (Refereed)
    Abstract [en]

    To date, the most promising scalable method for achieving 2D materials dispersions is through liquidbasedexfoliation of nanosheets in solvents. We study the use of high throughput shear exfoliation insteadof sonication to exfoliate water dispersions of MoS2 using environmental friendly stabilizers based oncellulose. The resulted dispersion was then concentrated and inkjet printed on a flexible substrate. We usedethyl cellulose, cellulose nanofibers (CNF) and ultra-fine cellulose nanofibers (UF-CNF). The stability wasevaluated by measuring the differences in concentration over time. The particle size distribution (PSD) ofthe dispersed particles was evaluated using statistical methods applied to SEM images of the dispersions(See Fig 1 and 2). The zeta potential and the mechanisms of stabilization involved was evaluated (See Fig4). All three stabilizers appear to work very well for MoS2 nanosheets even though the mechanisms ofstabilization were different i.e. steric stabilization for MoS2-EC and electrostatic stabilization for MoS2-CNF and MoS2-UF-CNF dispersions. For the MoS2-EC dispersions we achieved a broader PSD (Fig. 1)and higher stability. Thin nanosheets was observed from the SEM image of MoS2-EC dispersions depositedonto cellulose filters by vacuum filtration (Fig. 5) which demonstrated that the exfoliation technique usedwas successful. The estimated concentration of the MoS2-EC dispersion after 8 days of sample preparationwas 0.24 mg/mL, 77% of the initial concentration (see Fig. 6) and it was relatively steady after 40 days ofsample preparation (0.22 mg/mL). To adjust the concentration and the viscosity of the MoS2-EC dispersion,we concentrated it using a rotary evaporator solvent exchange technique. For this we used terpineol andadjusted the viscosity using ethanol. This paper presents the results of an inkjet 2D material ink usingenvironmental friendly components different than previous 2D materials inks that used organic solvents orwater based dispersions containing surfactants.

  • 6.
    Forsberg, Viviane
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Zhang, Renyun
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Hummelgård, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Olin, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Towards flexible and cheap printed electronics using inks of exfoliated 2D materials stabilized by cellulose2017Conference paper (Other academic)
    Abstract [en]

    Flexible and cheap electronics are needed for simple applications such as sensors and solar cells. To achieve this, thin functional materials should be deposited efficiently to flexible substrates such as paper. A promising method for the deposition of such materials is through inkjet printing that said a stable and printable dispersion is necessary. We achieved this through liquid-based exfoliation of 2D materials in water using shear exfoliation and cellulose stabilizers. The resulted dispersion was then concentrated and inkjet printed on a flexible substrate. We used ethyl cellulose, cellulose nanofibers (CNF) and ultra-fine cellulose nanofibers (UF-CNF). All three stabilizers appear to work very well for MoS2 nanosheets even though the mechanisms of stabilization were different among them. For the MoS2-EC dispersions we achieved a broader PSD and higher dispersion stability. Thin nanosheets were observed from the SEM image of MoS2-EC dispersions deposited onto cellulose filters. The estimated concentration of the MoS2-EC dispersion after 20 days of sample preparation was 0.20 mg/mL. This dispersion was further processed to adjust the concentration and viscosity.  Good coverage of the substrate was achieved after 50 printing passes. If the same technique is applied to other 2D materials such as graphene (conductor) and boro nitride (insulator), a transistor can be fabricated.

  • 7.
    Forsberg, Viviane
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Zhang, Renyun
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Hummelgård, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Olin, Håkan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Towards stable 2D materials inkjet inks: a study of stabilizers and MoS2 grades2017Conference paper (Refereed)
  • 8.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Measuring and producing high perceived whiteness2011In: Paper Technology, ISSN 0306-252X, Vol. 52, no 1, p. 15-17Article in journal (Other academic)
  • 9.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Quantum efficiency of fluorescent dyesin different furnishesManuscript (preprint) (Other academic)
    Abstract [en]

    A recently proposed model for the radiative properties of optically thick fluorescentturbid media of finite thickness (Kokhanovsky, JOSA A, 26(8), p1896) is successfullyapplied to uncoated papers produced at different thicknesses. It is found that thequantum efficiency of the FWA is almost independent of the fibre type, FWA type,FWA concentration and filler additive concentrations used in this study. The scatteringcoefficient is however dependent on the FWA concentration. The absorptioncoefficient depends on the adsorption of the FWA in the furnish and is function ofthe sample thickness and of the FWA type, at equal amount of FWA used in the papermakingprocess. The results open for a estimation of the model parameters asfunction of the FWA concentration and furnish. This is necessary in order to use themodel for optimizing fluorescence in the paper and textile industries.

  • 10.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Whiteness and Fluorescence in Layered Paper and Board: Perception and Optical Modelling2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is about modelling and predicting the perceived whiteness of plain paper from the paper composition, including fluorescent whitening agents. This involves psychophysical modelling of perceived whiteness from measurable light reflectance properties, and physical modelling of light scattering and fluorescence from the paper composition.

    Existing models are first tested and improvements are suggested and evaluated. A colour appearance model including simultaneous contrast effects (CIECAM02-m2), earlier tested on coloured surfaces, is successfully applied to perceived whiteness. An extension of the Kubelka-Munk light scattering model including fluorescence for turbid media of finite thickness is successfully tested for the first time on real papers. It is extended to layered constructions with different layer optical properties and modified to enable parameter estimation with conventional d/0° spectrophotometers used in the paper industry. Lateral light scattering is studied to enable simulating the spatially resolved radiance factor from layered constructions, and angle-resolved radiance factor simulations are performed to study angular variation of whiteness.

    It is shown that the linear CIE whiteness equation fails to predict the perceived whiteness of highly white papers with distinct bluish tint. This equation is applicable only in a defined region of the colour space, a condition that is shown to be not fulfilled by many commercial office papers, although they appear white to most observers. The proposed non-linear whiteness equations give to these papers a whiteness value that correlates with their perceived whiteness, while application of the CIE whiteness equation outside its region of validity overestimates perceived whiteness.

    It is shown that the fluorescence efficiency of FWA is essentially dependent only on the ability of the FWA to absorb light in its absorption band. Increased FWA concentration leads accordingly to increased whiteness. However, since FWA absorbs light in the violet-blue region of the electromagnetic spectrum, the reflectance factor decreases in that region with increasing FWA amount. This violet-blue absorption tends to give a greener shade to the paper and explains most of the observed greening and whiteness saturation at larger FWA concentrations. A red-ward shift of the quantum efficiency is observed with increasing FWA concentration, but this is shown to have a negligible effect on the whiteness value. The results are directly applicable to industrial applications for better instrumental measurement of whiteness and thereby optimising the use of FWA with the goal to improve the perceived whiteness.

  • 11.
    Gustafsson Coppel, Ludovic
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Whiteness and Fluorescence in Paper: Perception and Optical Modelling2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is about modelling and predicting the perceived whiteness of plain paper from the paper composition, including fluorescent whitening agents. This includes psycho-physical modelling of perceived whiteness from measurable light reflectance properties, and physical modelling of light scattering and fluorescence from the paper composition.

    Existing models are first tested and improvements are suggested and evaluated. The standardised and widely used CIE whiteness equation is first tested on commercial office papers with visual evaluations by different panels of observers, and improved models are validated. Simultaneous contrast effects, known to affect the appearance of coloured surfaces depending on the surrounding colour, are shown to significantly affect the perceived whiteness. A colour appearance model including simultaneous contrast effects  (CIECAM02-m2), earlier tested on coloured surfaces, is successfully applied to perceived whiteness. A recently proposed extension of the Kubelka-Munk light scattering model including fluorescence for turbid media of finite thickness is successfully tested for the first time on real papers.

    It is shown that the linear CIE whiteness equation fails to predict the perceived whiteness of highly white papers with distinct bluish tint. This equation is applicable only in a defined region of the colour space, a condition that is shown to be not fulfilled by many commercial office papers, although they appear white to most observers. The proposed non-linear whiteness equations give to these papers a whiteness value that correlates with their perceived whiteness, while application of the CIE whiteness equation outside its region of validity overestimates perceived whiteness.

    It is shown that the quantum efficiency of two different fluorescent whitening agents (FWA) in plain paper is rather constant with FWA type, FWA concentration, filler content, and fibre type. Hence, the fluorescence efficiency is essentially dependent only on the ability of the FWA to absorb light in its absorption band.  Increased FWA concentration leads accordingly to increased whiteness. However, since FWA absorbs light in the violet-blue region of the electromagnetic spectrum, the reflectance factor decreases in that region with increasing FWA amount. This violet-blue absorption tends to give a greener shade to the paper and explains most of the observed greening and whiteness saturation at larger FWA concentrations. A red-ward shift of the quantum efficiency is observed with increasing FWA concentration, but this is shown to have a negligible effect on the whiteness value.

    The results are directly applicable to industrial applications for better instrumental measurement of whiteness and thereby optimising the use of FWA with the goal to improve the perceived whiteness. In addition, a modular Monte Carlo simulation tool, Open PaperOpt, is developed to allow future spatial- and angle-resolved particle level light scattering simulation.

     

  • 12.
    Gustafsson Coppel, Ludovic
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Andersson, Mattias
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Edström, Per
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Kinnunen, Jussi
    Univ Eastern Finland, Dept Math & Phys, FI-80101 Joensuu, Finland.
    Limitations of the efficiency of fluorescent whitening agents in uncoated paper2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 3, p. 319-328Article in journal (Refereed)
    Abstract [en]

    The fluorescence efficiency of one fluorescent whitening agent (FWA) inuncoated and unfilled paper was characterised at different FWA concentrations. An extendedKubelka-Munk model proposed earlier by several authors was applied to quantify the effect onCIE whiteness of absorption of the FWA in the visible spectrum . At high FWA concentration,chemical interactions slightly modify the emission spectrum of the FWA, and the quantumefficiency depends on the FWA concentration. This effect has however a negligible effect onthe CIE whiteness for FWA concentrations used in practice. The overlap of the absorption andemission bands of the FWA is shown to be the main cause of greening (a shift of thechromaticity towards green) and saturation of the fluorescence effect. With increasing FWAconcentration, the positive effect of fluorescence is neutralised by the reduction of thereflectance factor in the violet-blue region of the spectrum induced by a significant absorptionof the FWA in that region.

  • 13.
    Hammarling, Krister
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Zhang, Renyun
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Manuilskiy, Anatoliy
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    FBG based upon evaporated Silica nano particles2011In: 1st EOS Topical Meetingon On Micro- and Nano-Optoelectronic Systems, Bremen, December 7-9, 2011, 2011Conference paper (Refereed)
    Abstract [en]

    A fiber bragg grating was made by evaporating silica nano particles on the outside of a multimode silica fiber core using EISA method. We demonstrate that a cost effective bragg filter may be built by evaporating nano particles directly on a fiber core, which is tunable with the particle size.

  • 14. Koptioug, Andrei
    Application of the Time-Variable Feedback to the Input Amplifiers of Pulse Magnetic Resonance Spectrometers: Theoretical Considerations2002In: Applied Magnetic Resonance, ISSN 0937-9347, E-ISSN 1613-7507, Vol. 22, no 22/4, p. 513-537Article in journal (Refereed)
    Abstract [en]

    Analytical model for the optimization of the signal-to-noise (S/N) performance for the receiverwith input resonance circuit and variable feedback is developed. It is shown that by varyingthe feedback type and depth optimization of the receiver the best S/N performance could be achieved.This approach is based upon a resonator-receiver model with lumped elements. These assumptionsare relatively general for the model to be applicable for the design of both continuous and pulsereceivers in radio-frequency and microwave bands. The overall S/N performance of the receiver uponthe noise properties of its elements and the feedback settings in the input amplifier is studied fordifferent parameter settings. It is shown that the separate optimization of individual elements doesnot necessarily lead to the best S/N performance of the receiver, especially when bandwidth propertiesand noise contribution of the elements are substantially different. It is shown that critical couplingof the amplifier to the resonance structure could be far from optimum. In some cases the optimumS/N performance could be achieved with the coupling settings less than critical. But under the assumptionsmade the coupling over the critical value does not correspond to the best receiver S/Nperformance. Suggestions on the optimum architecture of magnetic resonance spectrometer receiverswith variable feedback are made.

  • 15.
    Koptioug, Andrei
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering and Sustainable Development.
    New Transmission Line Resonators for ESE1998In: EPR Newsletter, Vol. 9, no 3, p. 20-22Article in journal (Other academic)
  • 16.
    Koptioug, Andrei
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Engineering, Physics and Mathematics.
    Antzutkin, Oleg
    Lindgren, M.
    Lund, Anders
    Optically detected ESR (OD ESR) of radical-ion pairs in coloured solutions: Observation of transient Trans-Azobenzene Radical Cation1993In: Applied Magnetic Resonance, ISSN 0937-9347, E-ISSN 1613-7507, Vol. 5, no 1, p. 77-86Article in journal (Refereed)
    Abstract [en]

    Trans-azobenzene dissolved in different liquid hydrocarbons absorbs fluorescence arising from all acceptors previously used in Fluorescence Detected Magnetic Resonance (FDMR) and Optically Detected ESR (OD ESR) spectroscopy making optical detection impossible. In this report a new acceptor,rubrene, having sufficient quantum yield of fluorescence in the red band 550–620 nm, has been proven successful. OD ESR spectra of the radical-ion pairtrans-azobenzene+/rubrene were detected in liquid squalane (2,6,10,15,19,23-hexamethyl-tetracosane) solution in the temperature range 294–243 K. The experimental isotropic hyperfine splittings of the radical cation oftrans-azobenzene (a N=1.4 mT) have been compared with those from MNDO/INDO calculations and with those of earlier work using freon matrix studies.

  • 17.
    Koptioug, Andrei
    et al.
    Department of Biomedical Physics and Bioengineering, University of Aberdeen, Aberdeen, UK.
    Foster, Margaret
    Grigor’ev, Igor
    Lurie, David
    Khramtsov, Valerij
    McCallum, S.
    Panagiotelis, I.
    Nicholson, I.
    In Vivo Detection of a pH-Sensitive Nitroxide in the Rat Stomach by Low-Field ESR-Based Techniques2003In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 49, no 3, p. 558-567Article in journal (Refereed)
    Abstract [en]

    A study was made of the in vivo detectability of a pH-sensitive, imidazolidine spin probe, and the efficacy of low-frequency electron spin resonance (ESR)-based techniques for pH measurement in vitro and in vivo in rats. The techniques used were longitudinally-detected ESR (LODESR) and field-cycled dynamic nuclear polarization (FC-DNP) for in vitro and in vivo measurements, and radiofrequency (RF)- and X-band ESR for comparisons in vitro. The spin probe was hexamethyl imidazolidine (HMI) with a pK of 4.6. All techniques detected HMI. Detection by FC-DNP implies coupling between the free radical and solvent water spins. Separations between the three spectral lines of the nitroxide radical, relative to measurement frequency, were consistent with theory. The overall spectrum width from unprotonated HMI (pH > pK) was greater than that from protonated agent (pH < pK). This was observed in vitro and in vivo. Longer-term studies showed that HMI is detectable and has the same spectral width (i.e., is at the same pH) up to 2 hr after gavage into the stomach, although the magnitude of the signal decreases rapidly during the first hour. These findings demonstrate the suitability of LODESR and FC-DNP for monitoring HMI and measuring pH in vivo. These techniques would be useful for monitoring disease and drug pharmacology in the living system.

  • 18. Koptioug, Andrei
    et al.
    Reijerse, Edward
    Klaassen, A. A. K.
    Application of Time-Variable Feedback to the Input Amplifier of Pulse Magnetic Resonance Spectrometers: Experimental Studies2002In: Applied Magnetic Resonance, ISSN 0937-9347, E-ISSN 1613-7507, Vol. 22, no 4, p. 455-473Article in journal (Refereed)
    Abstract [en]

    Experimental research on the improvement of the sensitivity and time resolution of pulsedmagnetic resonance spectrometers is discussed. It is shown that application of a time-variable feedbackof a signal to the input of the receiver amplifier can decouple the "fixed" relationship betweenthe quality factor Q and the ringdown time of the resonance system. Experiments were performedwith low-frequency, radio-frequency and microwave pulse-type magnetic resonance receivers. Modificationsof an S/C-band electron spin echo modulation spectrometer carried out to check the “timevariablefeedback” performance is described. It is demonstrated that application of a time-variablefeedback can significantly reduce the ringdown time and improve the recovery properties of the magneticresonance receiver system. It is also demonstrated that the time-variable feedback can improvethe overall receiver sensitivity due to the fact that working bandwidth of the resonance system canbe optimized separately for the transmit and receive modes. Signal values could be increased at leastthree times and the signal-to-noise ratio about 1.5–2 times. The largest improvement is achieved withthe initially overcoupled resonator. Experimental spectra of test samples for different settings of thetime-variable feedback are shown.

  • 19.
    Koptioug, Andrei
    et al.
    Department of Bio-Medical Physics and Bio-Engineering, University of Aberdeen, Foresterhill, Aberdeen AB9 2ZD, United Kingdom..
    Reijerse, Edward
    Klaassen, A. K.
    New Transmission-Line Resonator for Pulsed EPR1997In: Journal of magnetic resonance, ISSN 1090-7807, E-ISSN 1096-0856, no 125, p. 369-371Article in journal (Refereed)
  • 20.
    Koptioug, Andrei
    et al.
    Institute of Chemical Kinetics and Combustion, Novosibirsk 630090, USSR.
    Saik, Vladimir
    Anisimov, Oleg
    Molin, Yurij
    Quantum beats in singlet-triplet transitions of radical pairs induced by a radio-frequency field1990In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 165, no 2-3, p. 142-145Article in journal (Refereed)
    Abstract [en]

    This Letter reports on the experimental observation of quantum beats stimulated by a resonance radio-frequency field in the recombination luminescence of radical-ion pairs. The beat frequency for solutions of p-terphenyl in squalane increases linearly with rf-field amplitude in the range 1 to 10 G in a rotating frame. The beat frequency corresponds to the theoretically calculated one, with amplitude twice as low as the theoretical one. This is attributed to contributions from the recombination of spin-uncorrelated radical-ion pairs

  • 21.
    Koptioug, Andrei
    et al.
    aInstitute of Chemical Kinetics and Combustion, USSR Academy of Sciences, Novosibirsk 630090, USSR.
    Saik, Vladimir
    Anisimov, Oleg
    Molin, Yurij
    Antzutkin, Oleg
    Effect of External Magnetic Fields and Resonance Radio frequency Radiation on Radical Reactions1990In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 164, no 1-2, p. 200-204Article in journal (Refereed)
    Abstract [en]

    It is well known that an external magnetic field can affect the rate of singlet-triplet transitions in a radical pair and hence its recombination probability in liquid. Resonance radiofrequency (RF) radiation induces quantum beats in the kinetics of radical pair recombination. At high RF field amplitudes the singlet-triplet transitions in radical pairs can be efficiently suppressed.

  • 22. Koptyug, Andrey
    et al.
    Sörman, E.
    A Method of Altering the Modulation Type and frequency of Commercial ESR Spectrometers:  1994In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 5, no 7, p. 797-780Article in journal (Refereed)
    Abstract [en]

    A strategy of altering the modulation type and frequency of commercial continuous wave ESR spectrometers without changes in the main console is discussed. A simple converter unit, permitting the use of various external receivers, widening the possibilities for the basic commercial set-up is suggested. Block diagrams for altering the modulation frequency and type are presented and the use of boxcar averaging systems for the time-resolved experiments is discussed in detail. As an example of a successful application of this method, some results obtained with two different RYDMR accessories, based on the commercial CW ESR spectrometers, are discussed. X-band OD ESR studies of hydrocarbon solutions are illustrated by the spectra of p-xylene and trans-phenyl-propene radical cations, and methyl acrylate and trans-azabenzene radical ions, detected in situ under X-irradiation. Semiconductor studies are illustrated by CW and time-resolved X-band ODMR spectra of PGa-P3Y point defects as well as its OD ENDOR and ENDOR-induced ODMR spectra

  • 23.
    Mahmood, S.
    et al.
    Stockholm Univ, Dept Phys, SE-10691 Stockholm, Sweden.
    Orban, I.
    Stockholm Univ, Dept Phys, SE-10691 Stockholm, Sweden.
    Ali, S.
    Stockholm Univ, Dept Phys, SE-10691 Stockholm, Sweden.
    Glans, Peter
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Bleda, E. A.
    Marmara Univ, Dept Phys, TR-81040 Istanbul, Turkey.
    Altun, Z.
    Marmara Univ, Dept Phys, TR-81040 Istanbul, Turkey.
    Schuch, R.
    Stockholm Univ, Dept Phys, SE-10691 Stockholm, Sweden.
    RECOMBINATION RATE COEFFICIENTS OF BORON-LIKE Ne2013In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 771, no 2, p. Art. no. 78-Article in journal (Refereed)
    Abstract [en]

    Recombination of Ne5+ was measured in a merged-beam type experiment at the heavy-ion storage ring CRYRING. In the collision energy range 0-110 eV resonances due to 2s(2)2p -> 2s2p(2) (Delta n=0) and 2s(2)2p -> 2s(2)3l (Delta n=1), core excitations were observed. The experimentally derived rate coefficients agree well with the calculations obtained using AUTOSTRUCTURE. At low energies, recombination is dominated by resonances belonging to the spin-forbidden 2s2p(2)(P-4(J))nl series. The energy-dependent rate coefficients were convoluted with a Maxwell-Boltzmann electron energy distribution to obtain plasma recombination rate coefficients. The data from the literature deviate from the measured results at low temperature.

  • 24. Morozov, V. A.
    et al.
    Koptyug, Andrey
    Institute of Chemical Kinetics and Combustion, Institutskaya Street 3, 630090 Novosibirsk, Russia.
    Doktorov, A. B.
    Molin, Yurij
    Dynamic theory of optically detected electron-nuclear double resonance of radical pairs (OD ENDOR) in liquid solutions1992In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 165, no 2-3, p. 297-312Article in journal (Refereed)
    Abstract [en]

    The theory of optically detected ENDOR of radical pairs (RP) recombining in liquid solutions is developed without taking account of the processes of relaxation. The RP spin dynamics is analysed in detail under the conditions of resonant two-frequency pumping of electron and nuclear spins in the particular case of the RP with one and two magnetic equivalent nuclei. Theoretical comparison of the OD ENDOR technique and the OD NMR one shows the advantage of the former method in studying longlived RP

  • 25.
    Navarro-Fructuoso, Hector
    et al.
    Dept. of Optics, Univ. of Valencia, E-46100, Burjassot, Spain .
    Saavedra-Tortosa, G.
    Dept. of Optics, Univ. of Valencia, E-46100, Burjassot, Spain .
    Martinez-Corral, Manuel
    Dept. of Optics, Univ. of Valencia, E-46100, Burjassot, Spain .
    Sjöström, Mårten
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information and Communication systems.
    Olsson, Roger
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information and Communication systems.
    Extended depth-of-field in integral imaging by depth-dependent deconvolution2013Conference paper (Refereed)
    Abstract [en]

    Integral Imaging is a technique to obtain true color 3D images that can provide full and continuous motion parallax for several viewers. The depth of field of these systems is mainly limited by the numerical aperture of each lenslet of the microlens array. A digital method has been developed to increase the depth of field of Integral Imaging systems in the reconstruction stage. By means of the disparity map of each elemental image, it is possible to classify the objects of the scene according to their distance from the microlenses and apply a selective deconvolution for each depth of the scene. Topographical reconstructions with enhanced depth of field of a 3D scene are presented to support our proposal.

  • 26.
    Orban, Istvan
    et al.
    Stockholm University, Department of Physics.
    Loch, Stuart D
    Auburn University, Department of Physics.
    Glans, Peter
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences, Engineering and Mathematics.
    Böhm, Stefan
    Stockholm University, Department of Physics.
    Schuch, Reinhold
    Stockholm University, Department of Physics.
    Effects of spin-forbidden resonances on the recombination of Be-like Si and Be-like Ne2011In: Physics Scripta, ISSN 0031-8949, Vol. T144, p. Art. no. 014035-Article in journal (Refereed)
    Abstract [en]

    Recombination through doubly excited states that can be formed only through spin-flip of the excited electrons can give very strong contributions to the recombination rate of Be-like ions. We demonstrate this, in this paper, with the electron-ion recombination spectra of Be-like Ne(6+) and Be-like Si(10+), recently measured at the CRYRING storage ring. These resonances have significant effects on the plasma rate coefficients. We show that neglect or imprecise calculation of these resonances is responsible for large spreads observed between various theoretical results from the literature.

  • 27.
    Wiklund, Hanna
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Uesaka, Tetsu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of applied science and design.
    Simulations of shearing of capillary bridges2012In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 136, no 9, p. Art. no. 094703-Article in journal (Refereed)
    Abstract [en]

    Capillary bridges are considered as the major source of interaction forces acting in wet particulate systems. We study the dynamic shear resistance by using a lattice Boltzmann numerical scheme for a binary fluid. The shear resistance force showed very little dependence on surface tension and contact angle. Instead, the shear resistance is a dynamic phenomenon and a major contributing factor is the distortion of the flow field caused by the presence of interfaces. This distortion of the flow field is geometry-dependent: in smaller diameter bridges the proportion of this distorted flow field becomes larger and it makes a major contribution to the shear resistance force. In other words multiple bridges have an enhancement effect on shear resistance.

  • 28.
    Örtegren, Jonas
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Lindgren, Mikael
    Swedish Defence Research Establishment.
    Pyroelectric liquid crystalline polymers for second order nonlinear optics2002In: Recent Research Developments in Optics, 2 / [ed] S.G. Pandalai, India: Trivandrum Research Signpost , 2002, p. 53-88Chapter in book (Other academic)
1 - 28 of 28
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