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Neuman, Magnus
Publications (10 of 25) Show all publications
Gustafsson Coppel, L., Johansson, N. & Neuman, M. (2015). Angular dependence of fluorescence from turbid media. Optics Express, 23(15), 19552-19564
Open this publication in new window or tab >>Angular dependence of fluorescence from turbid media
2015 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 15, p. 19552-19564Article in journal (Refereed) Published
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.

National Category
Other Physics Topics
Identifiers
urn:nbn:se:miun:diva-24983 (URN)10.1364/OE.23.019552 (DOI)000361035300093 ()2-s2.0-84954492839 (Scopus ID)
Available from: 2015-05-26 Created: 2015-05-26 Last updated: 2017-12-04Bibliographically approved
Edvardsson, S., Neuman, M., Edström, P. & Olin, H. (2015). Solving equations through particle dynamics. Computer Physics Communications, 197, 169-181
Open this publication in new window or tab >>Solving equations through particle dynamics
2015 (English)In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 197, p. 169-181Article in journal (Refereed) Published
Abstract [en]

The present work evaluates a recently developed particle method (DFPM). The basic idea behind this method is to utilize a Newtonian system of interacting particles that through dissipation solves mathematical problems. We find that this second order dynamical system results in an algorithm that is among the best methods known. The present work studies large systems of linear equations. Of special interest is the wide eigenvalue spectrum. This case is common as the discretization of the continuous problem becomes dense. The convergence rate of DFPM is shown to be in parity with that of the conjugate gradient method, both analytically and through numerical examples. However, an advantage with DFPM is that it is cheaper per iteration. Another advantage is that it is not restricted to symmetric matrices only, as is the case for the conjugate gradient method. The convergence properties of DFPM are shown to be superior to the closely related approach utilizing only a first order dynamical system, and also to several other iterative methods in numerical linear algebra. The performance properties are understood and optimized by taking advantage of critically damped oscillators in classical mechanics. Just as in the case of the conjugate gradient method, a limitation is that all eigenvalues (spring constants) are required to be of the same sign. DFPM has no other limitation such as matrix structure or a spectral radius as is common among iterative methods. Examples are provided to test the particle algorithm’s merits and also various performance comparisons with existent numerical algorithms are provided.

Place, publisher, year, edition, pages
Elsevier, 2015
Keywords
Particle methods, Computational mechanics, Many-particle dynamics, System of linear equations, Dynamical functional particle method
National Category
Computational Mathematics
Identifiers
urn:nbn:se:miun:diva-26030 (URN)10.1016/j.cpc.2015.08.028 (DOI)000362919500018 ()2-s2.0-84942990585 (Scopus ID)
Available from: 2015-10-05 Created: 2015-10-05 Last updated: 2017-12-01Bibliographically approved
Neuman, M., Edvardsson, S. & Edström, P. (2015). Solving the radiative transfer equation with a mathematical particle method. Optics Letters, 40(18), 4325-4328
Open this publication in new window or tab >>Solving the radiative transfer equation with a mathematical particle method
2015 (English)In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 40, no 18, p. 4325-4328Article in journal (Refereed) Published
Abstract [en]

We solve the radiative transfer equation (RTE) using a recently proposed mathematical particle method, originally developed for solving general functional equations. We show that, in the case of the RTE, it gives several advantages, such as handling arbitrary boundary conditions and phase functions and avoiding numerical instability in strongly forward-scattering media. We also solve the RTE, including fluorescence, and an example is shown with a fluorescence cascade where light is absorbed and emitted in several steps. We show that the evaluated particle method is straightforward to implement, which is in contrast with many traditional RTE solvers, but a potential drawback is the tuning of the method parameters.

Place, publisher, year, edition, pages
Optical Society of America, 2015
National Category
Computational Mathematics
Identifiers
urn:nbn:se:miun:diva-26029 (URN)10.1364/OL.40.004325 (DOI)000361556700035 ()26371927 (PubMedID)2-s2.0-84957710820 (Scopus ID)
Available from: 2015-10-05 Created: 2015-10-05 Last updated: 2017-12-01Bibliographically approved
Johansson, N., Neuman, M., Andersson, M. & Edström, P. (2014). Influence of finite-sized detection solid angle on bidirectional reflectance distribution function measurements. Applied Optics, 53(6), 1212-1220
Open this publication in new window or tab >>Influence of finite-sized detection solid angle on bidirectional reflectance distribution function measurements
2014 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 53, no 6, p. 1212-1220Article in journal (Refereed) Published
Abstract [en]

This paper deals with limitations and often overlooked sources of error introduced in compact double-beam goniophotometers. It is shown that relative errors in measured radiance factor, comparable to the total measurement uncertainty, can be introduced if recommended corrections are not carried out. Two different error sources are investigated, both related to the size of the detection solid angle. The first is a geometrical error that occurs when the size of the illuminated area and detector aperture are comparable to the distance between them. The second is a convolution error due to variations in radiant flux over the detector aperture, which is quantified by simulating the full 3D bidirectional reflectance distribution function (BRDF) of a set of samples with different degrees of anisotropic reflectance. The evaluation is performed for a compact double-beam goniophotometer using different detection solid angles, and it is shown that both error sources introduce relative errors of 1%–3%, depending on viewing angle and optical properties of the sample. Commercially available compact goniophotometers, capable of absolute measurements, are becoming more and more common, and the findings in this paper are therefore important for anyone using or planning to use this type of instrument.

Place, publisher, year, edition, pages
Optical Society of America, 2014
Keywords
Reflection, Scattering measurements, BRDF, turbid media
National Category
Natural Sciences
Identifiers
urn:nbn:se:miun:diva-20949 (URN)10.1364/AO.53.001212 (DOI)000331949600027 ()2-s2.0-84942366011 (Scopus ID)
Available from: 2014-01-03 Created: 2014-01-03 Last updated: 2017-12-06Bibliographically approved
Neuman, M., Edvardsson, S. & Edström, P. (2013). A particle approach to the radiative transfer equation with fluorescence.
Open this publication in new window or tab >>A particle approach to the radiative transfer equation with fluorescence
2013 (English)Article in journal (Refereed) Submitted
National Category
Other Physics Topics
Identifiers
urn:nbn:se:miun:diva-18693 (URN)
Available from: 2013-04-04 Created: 2013-04-04 Last updated: 2016-12-09Bibliographically approved
Namedanian, M., Gustafsson Coppel, L., Neuman, M., Gooran, S., Edström, P., Kolseth, P. & Koh, W. (2013). Analysis of Optical and Physical Dot Gain by Microscale Image Histogram and Modulation Transfer Functions. Journal of Imaging Science and Technology, 57(2), 020504-1-020504-5
Open this publication in new window or tab >>Analysis of Optical and Physical Dot Gain by Microscale Image Histogram and Modulation Transfer Functions
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2013 (English)In: Journal of Imaging Science and Technology, ISSN 1062-3701, E-ISSN 1943-3522, Vol. 57, no 2, p. 020504-1-020504-5Article in journal (Refereed) Published
Abstract [en]

The color of a print is affected by ink spreading and lateral light scattering in the substrate, making printed dots appear larger. Characterization of physical and optical dot gain is crucial for the graphic arts and paper industries. We propose a novel approach to separate physical from optical dot gain by use of a high-resolution camera. This approach is based on the histogram of microscale images captured by the camera. Having determined the actual physical dot shape, we estimate the modulation transfer function (MTF) of the paper substrate. The proposed method is validated by comparing the estimated MTF of 11 offset printed coated papers to the MTF obtained from the unprinted papers using measured and Monte Carlo simulated edge responses.

National Category
Media Engineering
Identifiers
urn:nbn:se:miun:diva-20432 (URN)10.2352/J.ImagingSci.Technol.2013.57.2.020504 (DOI)000344138900004 ()2-s2.0-84886047298 (Scopus ID)
Available from: 2013-12-03 Created: 2013-12-03 Last updated: 2017-12-06Bibliographically approved
Neuman, M. (2013). Applied problems and computational methods in radiative transfer. (Doctoral dissertation). Härnösand: Mittuniversitetet
Open this publication in new window or tab >>Applied problems and computational methods in radiative transfer
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Härnösand: Mittuniversitetet, 2013. p. 25
Series
Mid Sweden University doctoral thesis, ISSN 1652-893X ; 151
National Category
Other Physics Topics
Identifiers
urn:nbn:se:miun:diva-19776 (URN)978-91-87103-80-3 (ISBN)
Public defence
2013-09-20, Alfhild Agrell-salen, Universitetsbacken 3, Härnösand, 10:00 (Swedish)
Opponent
Supervisors
Funder
Vinnova
Available from: 2013-09-16 Created: 2013-08-26 Last updated: 2013-09-16Bibliographically approved
Linder, T., Löfqvist, T., Gustafsson Coppel, L., Neuman, M. & Edström, P. (2013). Lateral light scattering in fibrous media. Optics Express, 21(6), 7835-7840
Open this publication in new window or tab >>Lateral light scattering in fibrous media
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2013 (English)In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 21, no 6, p. 7835-7840Article in journal (Refereed) Published
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.

Keywords
Radiative transfer, Halftone image reproduction, Multiple scattering, Turbid media
National Category
Other Physics Topics Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-18657 (URN)10.1364/OE.21.007835 (DOI)000316796000119 ()2-s2.0-84875750991 (Scopus ID)
Projects
PaperOpt
Funder
VinnovaThe Knowledge Foundation
Available from: 2013-03-28 Created: 2013-03-28 Last updated: 2017-12-06Bibliographically approved
Johansson, N., Neuman, M., Andersson, M. & Edström, P. (2013). Separation of surface and bulk reflectance by absorption of bulk scattered light. Applied Optics, 52(19), 4749-4754
Open this publication in new window or tab >>Separation of surface and bulk reflectance by absorption of bulk scattered light
2013 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 52, no 19, p. 4749-4754Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Optical Society of America, 2013
Keywords
Reflection, Scattering measurements, Turbid media
National Category
Other Physics Topics
Identifiers
urn:nbn:se:miun:diva-19640 (URN)10.1364/AO.52.004749 (DOI)000321289700043 ()2-s2.0-84879948231 (Scopus ID)
Available from: 2013-09-05 Created: 2013-07-26 Last updated: 2017-12-06Bibliographically approved
Neuman, M., Gustafsson Coppel, L. & Edström, P. (2012). A partial explanation of the dependence between light scattering and light absorption in the Kubelka-Munk model. Nordic Pulp & Paper Research Journal, 27(2), 426-430
Open this publication in new window or tab >>A partial explanation of the dependence between light scattering and light absorption in the Kubelka-Munk model
2012 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 27, no 2, p. 426-430Article in journal (Refereed) Published
Abstract [en]

The Kubelka-Munk scattering and absorption coefficients of a set of paper samples are assessed using reflectance measurements in d/0 geometry. The coefficients display the widely studied dependence between light scattering and light absorption, since the light scattering coefficient decreases in regions of high absorption. It is shown using general radiative transfer theory that part of this dependence can be explained and eliminated by taking into account the geometry of the d/0 instrument and the single scattering anisotropy, thus capturing the angular variations of the light reflected from the samples. These findings allow the papermaker to better predict the reflectance from mixtures of pulps, fillers, dye, and FWA, and to better evaluate bleaching efforts. 

Keywords
Anisotropic reflectance; Kubelka-Munk; Paper optics; Parameter dependence; Reflectance measurements
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:miun:diva-16873 (URN)10.3183/NPPRJ-2012-27-02-p426-430 (DOI)000315696000035 ()2-s2.0-84865251384 (Scopus ID)
Available from: 2013-04-04 Created: 2012-08-28 Last updated: 2017-12-07Bibliographically approved
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