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  • 1051.
    Yang, Qixing
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Erosion of refractory during gas injection: a cavitation based model1990Ingår i: Scandinavian journal of metallurgy, ISSN 0371-0459, E-ISSN 1600-0692, Vol. 19, nr 3, s. 127-137Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The problem of tuyere refractory wear has been studied in an air-water model using a 4 mm diameter tuyere. Erosion tests, with boric acid (H(3)BO(3)) disks as refractory simulators, and measurements of back-attack frequency were carried out. The erosion pattern showed two distinct features; isolated elliptical pits and a continuous irregular shear wear pattern. The influence of the surface hardness and gas flow rate on these features was investigated. Pitting was found most frequently on disks formed at the lowest pressure (10 tons), but for pressures greater than 20 tons little difference was seen between disks. When the gas flow was in the bubbling regime, pitting was observed inside the region closest to the tuyere tip, with a maximum at the transition to jetting flow. Occasionally, pits could still be observed when the gas flow rate was rather high (NMa=1.82). The irregular wear pattern appeared independent of disk surface properties, however, sensitive to the gas flow rate. In the bubble flow regime, the wear was seen only outside a certain radius, which corresponds well to the radius of the bubbles. In the jetting regime, the wear was also observed close to the tuyere. The disk weight loss showed a maximum in the bubbling-to-jetting transition region, where the back-attack frequency also reached a maximum. The results support the idea that cavitation erosion, through liquid microjet pitting, is the main mechanical wear agent. A model for the generation and

  • 1052.
    Yang, Qixing
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Industriell miljö- och processteknik.
    Gustavsson, Håkan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Buström, Eric
    Swerea MEFOS AB.
    Erosion of referactory during gas injection: a cavitation based model1989Ingår i: Scaninject V: 5th international conference on ladle metallurgy, Luleå, Sweden, June 6-8, 1989, MEFOS , 1989, Vol. I, s. 259-289Konferensbidrag (Refereegranskat)
    Abstract [en]

    The problem of tuyere refractory wear has been studied in an air--water model using a 4 mm diamter tuyere. Erosion tests, with boric acid (H sub 3 BO sub 3 ) disks as refactory simulators, and measurements of back-attack frequency were carried out. The erosion pattern shows two distinct features: isolated elliptical pits and a continuous irregular shear wear pattern. The influence on these features of the surface hardness and gas flow rate was investigated. 24 ref.--

  • 1053. Yousefi, Hossein
    et al.
    Ahmadian, Alireza
    Khodadad, Davood
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Saberi, Hooshangh
    Daneshmehr, Alireza
    An optimised linear mechanical model for estimating brain shift caused by meningioma tumours2013Ingår i: International Journal of Biomedical Science and Engineering, ISSN 2376-7227, Vol. 1, nr 1, s. 1-9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Estimation of brain deformation plays an important role in computer-aided therapy and image-guided neurosurgery systems. Tumour growth can cause brain deformation and change stress distribution in the brain. Biomechanical models exist that use a finite element method to estimate brain shift caused by tumour growth. Such models can be categorised as linear and non-linear models, both of which assume finite deformation of the brain after tumour growth. Linear models are easy to implement and fast enough to for applications such as IGS where the time is a great of concern. However their accuracy highly dependent on the parameters of the models in this paper, we proposed an optimisation approach to improve a naive linear model to achieve more precise estimation of brain displacements caused by tumour growth. The optimisation process has improved the accuracy of the model by adapting the brain model parameters according to different tomour sizes.We used patient-based tetrahedron finite element mesh with proper material properties for brain tissue and appropriate boundary conditions in the tumour region. Anatomical landmarks were determined by an expert and were divided into two different sets for evaluation and optimisation. Tetrahedral finite element meshes were used and the model parameters were optimised by minimising the mean square distance between the predicted locations of the anatomical landmarks derived from Brain Atlas images and their actual locations on the tumour images. Our results demonstrate great improvement in the accuracy of an optimised linear mechanical model that achieved an accuracy rate of approximately 92%.

  • 1054.
    Zipser, L.
    et al.
    HTW, Hochschule für Technik und Wirtschaft, Dresden.
    Franke, H.
    HTW, Hochschule für Technik und Wirtschaft, Dresden.
    Olsson, Erik
    Molin, Nils-Erik
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Ultrasound object fields in air reconstructed using digital phase conjugation2002Ingår i: Proceedings: 2002 IEEE Ultrasonics Symposium : October 8 - 11, 2002, Forum Hotel, Munich, Germany / [ed] Donald E. Yuhas, Piscataway, NJ: IEEE Communications Society, 2002, s. 765-768Konferensbidrag (Refereegranskat)
    Abstract [en]

    A scanning laser Doppler vibrometer is used to record 2D ultrasound fields in air. The laser light of the vibrometer traverses the sound field to and from a rigid reflector and determines the velocity field, a quantity proportional to the sound pressure rate, in each scanned point relative to the sound source. The object sound is the scattered field from objects outside the recording area. Digital reconstruction using phase conjugation (time reversal) of the object sound field is then performed and the original object field intensity and phase is reconstructed.

  • 1055.
    Zipser, Lothar
    et al.
    Hochschule für Technik/Wirtschaft, University of Applied Sciences, Friedrich-List-Platz.
    Franke, Heinz
    Hochschule für Technik/Wirtschaft, University of Applied Sciences, Friedrich-List-Platz.
    Olsson, Erik
    Molin, Nils-Erik
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Reconstructing two-dimensional acoustic object fields by use of digital phase conjugation of scanning laser vibrometry recordings2003Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 42, nr 29, s. 5831-5838Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    scanning laser Doppler vibrometer is used to record two-dimensional ultrasound fields in air. The laser light of the vibrometer traverses the sound field to and from a rigid reflector and determines the velocity field, a quantity proportional to the sound pressure rate, in each scanned point relative to the sound source. The object sound is the scattered field from objects outside the recording area. Digital reconstruction by use of phase conjugation (time reversal) of the object sound field is then performed, and the original object field intensity and phase is reconstructed

  • 1056.
    Åkerstedt, Hans
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Damping of transient energy growth of three-dimensional perturbations in hydromagnetic pipe flow1995Ingår i: Fluid Dynamics Research, ISSN 0169-5983, E-ISSN 1873-7005, Vol. 15, nr 5, s. 295-312Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The stability of infinitesimal three-dimensional perturbations in hydromagnetic pipe flow where the applied magnetic field is in the streamwise direction is considered. The study is limited to the case of small magnetic Reynolds numbers and the main objective of the paper is to study the transient evolution of the kinetic energy. A general effect of the magnetic field is to increase the damping of the eigenvalues of the individual perturbation modes. For the case of infinitely long perturbations, which in the non-magnetic case has been found to have the largest transient growth, the magnetic field perturbations are decoupled from the flow and there is no effect on the stability properties of the flow. For shorter waves, and for moderate values of the interaction parameter (I = RmA2 ≈ 1-3) the hydromagnetic damping effect on the transient energy growth is, however, substantial, especially for small azimuthal mode numbers n. (Here Rm is the magnetic Reynolds number and A is the Alfvén number.) This parameter range has been found in experiments to give significantly higher transitional Reynolds numbers (Fraim and Heiser, 1968). Since the hydromagnetic damping effect is weak for long waves and large for shorter waves, the implications of the results to ordinary pipe flow is that the energy growth found for short waves may be more crucial as a mechanism for transition than the corresponding growth for longer waves.

  • 1057.
    Åkerstedt, Hans
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Jansson, Ida
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    The stability of a flexibly mounted rotating cylinder in turbulent annular flow2015Ingår i: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 58, s. 152-172Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we determine the inviscid linear stability with respect to two-dimensional disturbances of a fluid flow between two concentric cylinders. The inner rigid cylinder rotates with the angular velocity Ω0 and is fixed on elastic hinges at each end in the transverse direction. The outer cylinder does not rotate and is rigidly fixed. We assume that the fluid flow has an inner core that rotates as a solid body with angular velocity Ω0/2 and outside the core there are turbulent boundary layers. The velocity profile of the turbulent boundary layers satisfies the viscous Camassa−Holm equations. The perturbed fluid flow is derived from Rayleigh’s equation. The analysis yields an equation of motion of the cylinder equivalent to previous work without boundary layers and a basic flow of constant angular vorticity. The analysis is not restricted to a small gap between the cylinders. The results are compared with the results by Antunes et al. (1996), who consider a similar problem with uniform velocity profile and the limit of small gap. For ρc/ρf<1ρc/ρf<1 the results disagree in that the present analysis shows stability whereas Antunes et al. find instability. For ρc/ρf>1ρc/ρf>1 both theories predict stability and for larger values of ρc/ρfρc/ρf the agreement is good especially for small gap.

  • 1058.
    Åkerstedt, Hans
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan
    Högberg, Sofie
    Electrostatic filtration of air-borne nano-particles2007Ingår i: Journal of Nanostructured Polymers and Nanocomposites, ISSN 1790-4439, Vol. 3, nr 4, s. 111-115Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Due to potential danger of nanoparticles for human health it is necessary to have control of their motion in air. Mechanical filtering is tricky since the particles are very small and alternative means to guide and collect them, need to be developed. Hence, in this paper clusters of carbon nanotubes are allowed to move through an electrical field generated by two parallel electrodes and it is shown that the tubes are strongly affected by this field and move swiftly towards the electrodes. Once hitting one of them most of the clusters leave towards the other electrode, the procedure is repeated and very few particles are collected. By putting an electrically insulating layer on one plate the particles however get stuck. This implies that the method investigated is an efficient method to collect air-borne carbon nanotubes

  • 1059.
    Åkerstedt, Hans O.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Deposition of charged nano-particles in the human airways including effects from cartilaginous rings2011Ingår i: Natural Science, ISSN 2150-4091, E-ISSN 2150-4105, Vol. 3, nr 10, s. 885-888Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents a numerical study of the deposition of spherical charged nano-particles caused by convection, Brownian diffusion and electrostatics in a pipe with a cartilaginous ring structure. The model describes the deposition of charged particles in the different generations of the tracheobronchial tree of the human lung. The upper airways are characterized by a certain wall structure called cartilaginous rings which modify the particle deposition when compared to an airway with a smooth wall. The problem is defined by solving Naver-Stokes equations in combination with a convective-diffusion equation and Gauss law for electrostatics. Three non- dimensional parameters describe the problem, the Peclet number Pe = 2ūa/D , the Reynolds number Re = ūa/v and an electrostatic parameter α=α2c0q2/(4ε0κT) . Here U is the mean velocity, a the pipe radius and D the diffusion coefficient due to Brownian motion given by D=κTCu/3πμd , where Cu is the Cunningham-factor Cu=1+λ/d(2.34+1.05exp(-0.39d/λ)) Here d is the particle diameter and λ the mean free path of the air molecules. Results are provided for generations G4-G16 of the human airways. The electrostatic parameter is varied to model different concentrations and charge numbers

  • 1060.
    Åkerstedt, Hans O.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Deposition of submicron charged particles in turbulent pipe flow with an application to trachea2018Ingår i: The International Journal of Multiphysics, ISSN 1750-9548, E-ISSN 2048-3961, Vol. 12, nr 1, s. 9-25Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper presents a study of the deposition of submicron charged spherical particles caused by convection, Brownian and turbulent diffusion in a pipe with a smooth wall and with a cartilaginous ring wall structure. The model is supposed to describe deposition of charged particles in generation 0 (trachea) of the human respiratory airways. The flow is modeled with a SST-turbulence model combined with a convective-diffusion equation including electric field migration for the particles, and Poisson’s equation for the determination of the electrostatic potential in terms of the space-charge density of the particles. An approximate analytical solution is derived for the case of a smooth pipe which is used to verify the numerical solutions obtained from using the commercial software Comsol Multiphysics. Numerical results of deposition rates are also provided for the case of a pipe with a cartilaginous ring wall structure.

  • 1061.
    Åkerstedt, Hans O.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Eller, Sebastian
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Lundström, Staffan T.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Numerical Investigation of Turbulent Flow through Rectangular and Biconvex Shaped Trash Racks2017Ingår i: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 9, nr 5, s. 412-426, artikel-id 76642Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Turbulent flow through a trash rack of bars of rectangular and biconvex shapes is considered. A trash rack is composed of an array of bars fitted into a hydro-electric power station to prevent debris and fish to enter the waterway towards the turbine. The work is directed towards modeling a large number of bars for which the flow turn out to have a periodic structure. It is here shown that this case can be simplified with the flow past a single bar together with periodic boundary conditions. Using this approach the head loss is derived for different angles of attack α and blockages P for two shapes of the rack, a rectangular bar and an aerodynamically shaped biconvex bar. It is found that overall loss of the biconvex bars is in general about 15% of the loss for the rectangular case for small angles of attack. For large angle of attack this difference diminishes. Of interest for the biconvex bars is also a local minimum in the head loss for angles approximately greater than 20˚ and for a blockage P around 0.35. This combination of parameters gives a low loss together with an efficient barrier for debris and fishes.

  • 1062.
    Åkerstedt, Hans O.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Högberg, Sofie
    Lundström, Staffan
    Sandström, Tomas
    Umeå universitet.
    The effect of cartilaginous rings on particle deposition by convection and Brownian diffusion2010Ingår i: Natural Science, ISSN 2150-4091, E-ISSN 2150-4105, Vol. 2, nr 7, s. 769-779Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A finite volume method for the numerical solution of viscoelastic flows is given. The flow of a differential upper-convected Maxwell (UCM) fluid through a contraction channel has been chosen as a prototype example. The conservation and constitutive equations are solved using the finite volume method (FVM) in a staggered grid with an upwind scheme for the viscoelastic stresses and a hybrid scheme for the velocities. An enhanced-in-speed pressure-correction algorithm is used and a method for handling the source term in the momentum equations is employed. Improved accuracy is achieved by a special discretization of the boundary conditions. Stable solutions are obtained for higher Weissenberg number (We), further extending the range of simulations with the FVM. Numerical results show the viscoelasticity of polymer solutions is the main factor influencing the sweep efficiency.

  • 1063.
    Åkerstedt, Hans O.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Högberg, Sofie
    Lundström, T. Staffan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    An asymptotic approach of Brownian deposition of nanofibres in pipe flow2013Ingår i: Theoretical and Computational Fluid Dynamics, ISSN 0935-4964, E-ISSN 1432-2250, Vol. 27, nr 5, s. 561-575Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An asymptotic approach is considered for the transport and deposition of nanofibres in pipe flow. Convection and Brownian diffusion are included, and Brownian diffusion is assumed to be the dominant mechanism. The fibre position and orientation are modelled with a probability density function for which the governing equation is a Fokker-Planck equation. The focus is set on dilute fibres concentrations implying that interaction between individual fibres is neglected. At the entrance of the pipe, a fully developed velocity profile is set and it is assumed that the fibres enter the pipe with a completely random orientation and position. A small parameter {Mathematical expression} is introduced, where l is the fibre half-length and a is the pipe radius. The probability density function is expanded for small {Mathematical expression} and the solution turns out to be multi-structured with three areas, consisting of one outer solution and two boundary layers. For the deposition of fibres on the wall, it is found that for parabolic flow, and for the lowest order, the deposition can be obtained with a simplified angle averaged convective-diffusion equation. It is suggested that this simplification is valid also for more complex flows like when the inflow boundary condition yields a developing velocity profile and flows within more intricate geometries than here studied. With the model fibre, deposition rates in human respiratory airways are derived. The results obtained compare relatively well with those obtained with a previously published model

  • 1064.
    Åkerstedt, Hans O.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Löfgren, Hans B
    Luleå tekniska universitet.
    Free surface magnetohydrodynamic flow with solidification2003Ingår i: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 22, nr 6, s. 581-601Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper considers an analysis of a liquid metal flow, occurring in the horizontal belt strip casting process. The liquid metal flows over a moving copper belt with a growing solidifying phase beneath the melt. The effect of applying a transverse magnetic field is investigated. A set of three-dimensional shallow water equations is derived. Supercritical flow is assumed and the shallow water equations are solved numerically using a shock-capturing method, which automatically takes care of the possibility of oblique hydraulic jumps.It is shown that non-uniform conditions introduced in the feeding region give a pattern of steady hydraulic jumps, which propagate downstream and are reflected at the sidewalls. The effect of the magnetic field is to brake the flow and damp the standing hydraulic jump pattern. Different feeding methods are compared and it is shown that the magnetic field erases the initial differences in liquid distribution using different feeding techniques

  • 1065.
    Åkerstedt, Hans O.
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Nycander, J.
    Department of Technology, Euratom–NFR Fusion Association, Uppsala University.
    Pavlenko, V.P.
    Department of Technology, Euratom–NFR Fusion Association, Uppsala University.
    Three-dimensional stability of drift vortices1996Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 3, nr 1, s. 160-167Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The three-dimensional stability of drift vortices that are two-dimensionally stable in the framework of the Hasegawa-Mima equation is studied. The three-dimensionality is caused by a coupling of the vortex to ion-acoustic waves that propagate along the magnetic field. It is concluded that this coupling does not significantly destabilize the vortex. A general stability criterion is derived that guarantees stability if the ratio between the parallel wave number k and the azimuthal mode number m is large enough. It is also found that no instability exists in the limit k→ 0 if the potential vorticity is a strictly decreasing function of r. Such profiles are typical for vortices that are two-dimensionally stable. Some particular profiles where the potential vorticity vanishes outside some radius are also examined. In one case an instability with m=1 is found, but a numerical solution of the eigenvalue problem shows that the maximum growth rate is very small, three orders of magnitude smaller than the angular velocity of the vortex flow.

  • 1066.
    Åstrand, Anders P.
    et al.
    Umeå University. Department of Applied Physics and Electronics.
    Jalkanen, Ville
    Umeå University. Department of Applied Physics and Electronics.
    Andersson, Britt M.
    Umeå University. Department of Applied Physics and Electronics.
    Lindahl, Olof
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Detection of stiff nodules embedded in soft tissue phantoms, mimicking cancer tumours, using a tactile resonance sensor2014Ingår i: Journal of Biomedical Science and Engineering, ISSN 1937-6871, E-ISSN 1937-688X, Vol. 7, nr 4, s. 181-193Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: Prostate cancer (PCa) is the most common form of cancer among males in Europe and in the USA and the most common curative treatment is removal of the prostate, i.e. prostatectomy. After the removal, the prostate is histopathologically analysed. One area of interest is to examine the perifery of the prostate, as tumours on and near the surface can indicate that the PCa has spread to other parts of the body. There are no current methods to examine the surface of the prostate at the time of surgery. Tactile resonance sensors can be used for detecting areas of different stiffness in soft tissue. Human prostate tissue affected by cancer is usually stiffer than healthy tissue, and for this purpose, a tactile resonance sensor was developed. The aim of this study was to investigate the depth at which embedded stiffer volumes could be detected, using soft tissue phantoms. Methods: With the tactile resonance sensor used in this study, the shift of the resonance frequency and the force at contact with tissue can be measured, and combined into a tissue stiffness parameter. The detection sensitivity of the sensor at impression depths, 0.4 and 0.8 mm, was measured for detection of inserted nodules of stiff silicone in softer silicone and in chicken muscle tissue, mimicking prostate tissue with cancer tumours. Results: Measurements on the silicone samples detected the hidden stiffer object at a depth of 1 - 4 mm with a difference in the stiffness parameter of 80 - 900 mN/kHz (p < 0.028, n = 48). At the depth 5 - 6 mm the difference was smaller but still significant < 30 mN/kHz (p < 0.05, n = 24). For the measurements on chicken muscle, the detectable depth was 4 mm (p < 0.05, n = 24). Conclusion: This model study suggests that, with only a small impression depth of ≤1 mm, the resonance sensor system described here can detect stiffness variations located at least 4 mm in silicone and chicken muscle, mimicking tumours in prostate tissue.

  • 1067.
    Åström, E.
    et al.
    LKAB R&D, Luleå.
    Bonomi, Germano
    Department of Mechanical and Industrial Engineering, University of Brescia.
    Calliari, Irene
    Department of Industrial Engineering, University of Padova.
    Calvini, Piero
    Department of Physics, University of Genova and Sezione INFN di Genova.
    Checchia, Paolo
    INFN Sezione di Padova.
    Donzella, Antonietta
    Department of Mechanical and Industrial Engineering, University of Brescia.
    Faraci, E.
    Centro Sviluppo Materiali SPA, Rome.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gonella, F.
    INFN Sezione di Padova.
    Hu, X.
    Swerea MEFOS AB, Luleå.
    Klinger, Joel A.
    INFN Sezione di Padova.
    Sundqvist Ökvist, Lena
    Swerea MEFOS AB, Luleå.
    Pagano, Davide
    Department of Mechanical and Industrial Engineering, University of Brescia.
    Rigoni, Andrea
    Department of Physics and Astronomy, University of Padova.
    Ramous, Emilio
    Department of Industrial Engineering, University of Padova.
    Urbani, M.
    Department of Physics and Astronomy, University of Padova.
    Vanini, Sara
    Department of Physics and Astronomy, University of Padova.
    Zenoni, Aldo
    Department of Mechanical and Industrial Engineering, University of Brescia.
    Zumerle, Gianni
    Department of Physics and Astronomy, University of Padova.
    Precision measurements of linear scattering density using muon tomography2016Ingår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 11, nr P7010Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrate that muon tomography can be used to precisely measure the properties of various materials. The materials which have been considered have been extracted from an experimental blast furnace, including carbon (coke) and iron oxides, for which measurements of the linear scattering density relative to the mass density have been performed with an absolute precision of 10%. We report the procedures that are used in order to obtain such precision, and a discussion is presented to address the expected performance of the technique when applied to heavier materials. The results we obtain do not depend on the specific type of material considered and therefore they can be extended to any application

  • 1068.
    Öhman, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    3D localization in digital holography from scattered light from micrometer-sized particles2018Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    When a particle is illuminated by a beam of light it will scatter and redistribute the light in all directions. How it scatters depends on the size, shape and refractive index of the particle. Additionally, it depends on the wavelength and polarization of the illuminating beam. The direction and distance to the observer relative the particle also needs to be considered.  A digital holographic imaging system is used to collect parts of the scattered light from micrometer-sized particles. By utilizing digital holography a three-dimensional reconstruction of the imaged scene is possible. Traditionally, particles are localized based on the intensity in the holographic reconstructions. In this licentiate thesis, the phase response of the scattered light is investigated and utilized. An alternative method for locating spherical particles is presented. The method locate particles based on a simple feature of a propagating wave, namely the fact that the wavefront curvature changes from converging to diverging at the axial location of the particle. The wavefront curvature is estimated using two different methods. The first method estimates the lateral phase-gradients using a finite-difference method. The second method uses a three-dimensional parametric model based on a Chebyshev polynomial expansion. The methods are demonstrated using both simulations and experimental measurements. The simulations are based on the Lorenz-Mie scattering theory for spherical particles and are combined with an imaging system model. Experiments are performed using an off-axis polarization sensitive digital holographic system with a coherent Nd:YAG laser. Measurements of stationary particles are made to validate and evaluate the proposed method. It is found that these methods estimate the true axial position and does not have the offset that is associated with intensity-based methods. Additionally, it is possible to exclude noise that shows up as false particles since noise does not have the same phase response as a real particle. The second method, that uses a parametric model, also improves the standard deviation in the positioning.

  • 1069.
    Öhman, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Polarization-resolved dual-view holographic system for 3D inspection of scattering particles2019Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 58, nr 34, s. G31-G40Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel dual-view polarization-resolved pulsed holographic system for particle measurements is presented. Both dual-view configuration and polarization-resolved registration are well suited for particle holography. Dual-view registration improves the accuracy in the detection of 3D position and velocities, and polarization-resolved registration provides polarization information about individual particles. The necessary calibrations are presented, and aberrations are compensated for by mapping the positions in the two views to positions in a global coordinate system. The system is demonstrated on a sample consisting of 7 μm spherical polystyrene particles dissolved in water in a cuvette. The system is tested with different polarizations of the illumination. It is found that the dual view improves the accuracy significantly in particle tracking. It is also found that by having polarization-resolved holograms, it is possible to separate naturally occurring sub-micrometer particles from the larger, 7 μm seeding particles.

  • 1070.
    Öhman, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Axial Particle Positioning by Wavefront Parameterization using Chebyshev Polynomials and Off-axis Digital Holography2017Ingår i: Digital Holography and Three-Dimensional Imaging, Washington: The Optical Society , 2017, artikel-id M4A.3Konferensbidrag (Refereegranskat)
    Abstract [en]

    A particle can be axially positioned where its scattered light has a plane wavefront. The phase anomaly compared to a plane wave is fitted to 3D Chebyshev polynomial, where coefficients correspond to the axial position.

  • 1071.
    Öhman, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Improved particle position accuracy from off-axis holograms using a Chebyshev model2018Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 57, nr 1, s. A157-A163Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Side scattered light from micrometer-sized particles is recorded using an off-axis digital holographic setup. From holograms, a volume is reconstructed with information about both intensity and phase. Finding particle positions is non-trivial, since poor axial resolution elongates particles in the reconstruction. To overcome this problem, the reconstructed wavefront around a particle is used to find the axial position. The method is based on the change in the sign of the curvature around the true particle position plane. The wavefront curvature is directly linked to the phase response in the reconstruction. In this paper we propose a new method of estimating the curvature based on a parametric model. The model is based on Chebyshev polynomials and is fit to the phase anomaly and compared to a plane wave in the reconstructed volume. From the model coefficients, it is possible to find particle locations. Simulated results show increased performance in the presence of noise, compared to the use of finite difference methods. The standard deviation is decreased from 3–39 μm to 6–10 μm for varying noise levels. Experimental results show a corresponding improvement where the standard deviation is decreased from 18 μm to 13 μm.

  • 1072.
    Öhman, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Off-axis digital holographic particle positioning based on polarization-sensitive wavefront curvature estimation2016Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 55, nr 27, s. 7503-7510Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Poor axial resolution in holographic particle imaging applications makes particle positioning in 3D space morecomplex since the positions are not directly obtained. In this paper we estimate the axial position of micrometerparticles by finding the location where the wavefront curvature from the scattered light becomes zero. By record-ing scattered light at 90°using off-axis holography, the complex amplitude of the light is obtained. Byreconstruction of the imaged scene, a complex valued volume is produced. From this volume, phase gradientsare calculated for each particle and used to estimate the wavefront curvature. From simulations it is found that thewavefront curvature became zero at the true axial position of the particle. We applied this metric to track an axialtranslation experimentally using a telecentric off-axis holographic imaging system with a lateral magnification ofM1.33. A silicon cube with molded particles inside was used as sample. Holographic recordings are performedboth before and after a 100μm axial translation. From the estimated positions, it was found that the mean dis-placement of particles between recordings was 105.0μm with a standard deviation of 25.3μm.

  • 1073.
    Öhman, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Polarization Resolved Dual-View Holographic System for Investigation of Microparticles2019Ingår i: OSA Technical Digest (Optical Society of America, 2019), 2019, artikel-id Th2A.5Konferensbidrag (Refereegranskat)
    Abstract [en]

    A dual-view polarization resolved digital-holographic system is presented. The necessary calibration for both polarization and spatial coordinates are outlined. As an example the system is is used to track spherical microparticles in a cuvette.

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