Arne Torbjørn Skjeltorp

• Skjeltorp, Arne Torbjørn; Dommersnes, Paul Gunnar & Høyer, Henrik (2017). New forceful magnetic bioseparation using GIAMAG Magnet Systems. MRS Advances.  ISSN 2059-8521.  2(24), s 1297- 1301 . doi: 10.1557/adv.2017.113 Full text in Research Archive.
• Cernák, Jozef; Helgesen, Geir; Skjeltorp, Arne Torbjørn; Kovác, Jozef; Voltr, Josef & Cizmar, Erik (2013). Magnetic properties of carbon nanodisk and nanocone powders. Physical Review B. Condensed Matter and Materials Physics.  ISSN 1098-0121.  87(1) . doi: 10.1103/PhysRevB.87.014434
• Helgesen, Geir; Knaapila, Matti; Skjeltorp, Arne Torbjørn; Høyer, Henrik & Cernak, J (2012). Field induced microparticle structure formation in fluids. Revista Cubana de Física.  ISSN 0253-9268.  29(1E34)
• Lukin, A.A.; Il'yashenko, E. I.; Skjeltorp, Arne Torbjørn & Helgesen, Geir (2012). Improvement of thermal stability of Nd-Tb-Fe-Co-B sintered magnets by additions of Pr, Ho, Al, and Cu. Physics Research International.  ISSN 2090-2220. . doi: 10.1155/2012/416717
• Knaapila, M.; Høyer, Henrik; Svåsand, Eldrid; Buchanan, Mark; Skjeltorp, Arne Torbjørn & Helgesen, Geir (2011). Aligned Carbon Cones in Free-Standing UV-Curable Polymer Composite. Journal of Polymer Science Part B: Polymer Physics.  ISSN 0887-6266.  49(6), s 399- 403 . doi: 10.1002/polb.22198
• Knaapila, Matti; Pinheiro, Jean Patrick; Buchanan, Mark; Skjeltorp, Arne Torbjørn & Helgesen, Geir (2011). Directed assembly of carbon nanocones into wires with an epoxy coating in thin films by a combination of electric field alignment and subsequent pyrolysis. Carbon.  ISSN 0008-6223.  49(10), s 3171- 3178 . doi: 10.1016/j.carbon.2011.03.039
• Knaapila, Matti; Svåsand, Eldrid; Pinheiro, Jean Patrick; Martinsen, Ørjan Grøttem; Buchanan, Mark; Skjeltorp, Arne Torbjørn; Helgesen, Geir & Rømoen, Ola Taarud (2011). Conductivity Enhancement in Carbon Nanocone Adhesive by Electric Field Induced Formation of Aligned Assemblies. ACS Applied Materials & Interfaces.  ISSN 1944-8244.  3(2), s 378- 384 . doi: 10.1021/am100990c
• Svåsand, Eldrid; Kristiansen, Kai de Lange; Martinsen, Ørjan Grøttem; Helgesen, Geir; Grimnes, Sverre & Skjeltorp, Arne Torbjørn (2009). Behavior of carbon cone particle dispersions in electric and magnetic fields. Colloids and Surfaces A: Physicochemical and Engineering Aspects.  ISSN 0927-7757.  339(1-3), s 211- 216 . doi: 10.1016/j.colsurfa.2009.02.025
• Helgessen, G; Svåsand, Eldrid & Skjeltorp, Arne Torbjørn (2008). Nanoparticle induced self-assembly. Journal of Physics: Condensed Matter.  ISSN 0953-8984.  20 . doi: 10.1088/0953-8984/20/20/204127
• Kristiansen, Kai de Lange; Svåsand, Eldrid; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2007). Interactions, Dynamics and Self-assembly of Magnetic Holes. Materials Research Society Symposium Proceedings.  ISSN 0272-9172.  947E Show summary

  Nonmagnetic microspheres dispersed in a ferrofluid are denoted magnetic holes. When the spheres are confined to a monolayer between two plane, parallel plates and subjected to AC magnetic fields, they show a variety of dynamical behaviors and assemblages. The magnetic interactions between the particles and their dynamical behavior are influenced by the boundaries and the degree of confinement. We have derived analytical results for the pair-wise competing interactions, and these compare favorably with experimental results. It is also possible to characterize the self-assembly and dynamics of the spheres by the theory of braids. It involves classifying different ways of tracing curves in space. The essentially two-dimensional motion of a sphere can be represented as a curve in a three-dimensional space-time diagram, and so several spheres in motion produce a set of braided curves. The dynamical modes can then be described in terms of braid-words. We also present a few other examples on how this system can be used to study dynamical processes.

• Svåsand, Eldrid; Helgesen, G & Skjeltorp, Arne Torbjørn (2007). Chain formation in a complex fluid containing carbon cones and disks in silicon oil. Colloids and Surfaces A: Physicochemical and Engineering Aspects.  ISSN 0927-7757.  308, s 67- 70 . doi: 10.1016/j.colsurfa.2007.05.030
• Svåsand, Eldrid; Skjeltorp, Arne Torbjørn; Akselvoll, J & Helgesen, G (2007). Local viscosity measurements using oscillating magnetic holes. Journal of Applied Physics.  ISSN 0021-8979.  101 . doi: 10.1063/1.2710300
• Heiberg-Andersen, H.; Helgesen, Geir; Knudsen, K.; Pinheiro, J.P.; Svåsand, Eldrid & Skjeltorp, Arne Torbjørn (2006). Nanocones - a different form of carbon with unique properties. Materials Research Society Symposium Proceedings.  ISSN 0272-9172.  901E, s 34.1- 34.8
• Il'yashenko, EI; Glebov, VA; Glebov, AV; Skjeltorp, Arne Torbjørn & Johansen, Tom Henning (2006). Permanent magnet systems with strong stray magnetic fields and very high gradients for material separation. Physica status solidi. A, Applied research.  ISSN 0031-8965.  203, s 1556- 1560
• Kristiansen, Kai de Lange; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2006). Braid theory and Zipf-Mandelbrot relation used in microparticle dynamics. European Physical Journal B : Condensed Matter Physics.  ISSN 1434-6028.  51, s 363- 371 . doi: 10.1140/epjb/e2006-00241-7
• Kristiansen, Kai de Lange; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2006). Braided Space-Time Particle Networks, In Arne Torbjørn Skjeltorp & Alexander V Belushkin (ed.),  Dynamics of Complex Interconnected Systems: Networks and Bioprocesses.  Springer Science+Business Media B.V..  ISBN 978-1-4020-5028-2.  9.  s 147 - 162
• Heiberg-Andersen, H.; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2005). Stability of Carbon Nanocones. Journal of Mathematical Chemistry.  ISSN 0259-9791.  38, s 589- 589
• Helgesen, Geir; Knudsen, Kenneth D. & Skjeltorp, Arne Torbjørn (2005). Den evigvarende energistrømmen, I: Gaute Einevold & Eirik Newth (red.),  Naturens kode.  Gyldendal Akademisk.  ISBN 82-05-34539-2.  Kapittel 12.  s 177 - 195
• Kristiansen, Kai de Lange; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2004). Experimental observation of Zipf-Mandelbrot relation. Physica A: Statistical Mechanics and its Applications.  ISSN 0378-4371.  335(3-4), s 413- 420 Show summary

  We study the dynamics of a few-body system of microparticles using rank-ordering statistics. This dynamical system is made up of micrometer sized plastic spheres dispersed in a ferrofluid driven by external magnetic fields. The world lines of the microspheres are captured and the dynamical modes are described by mathematical braid theory. Rank-ordering statistics on these modes shows a large power law region consistend with the Zipf-Mandelbrot relation.

• Toussaint, Renaud; Akselvoll, Jørgen; Helgesen, Geir; Flekkøy, Eirik Grude & Skjeltorp, Arne Torbjørn (2004). Interactions of magnetic holes in ferrofluid layers. Colloid and Polymer Science.  ISSN 0303-402X.  128
• Kristiansen, Kai de Lange; Helgesen, G & Skjeltorp, Arne Torbjørn (2004). Braid theory and Zipf relation used in dynamics of magnetic microparticles. Journal of Magnetism and Magnetic Materials.  ISSN 0304-8853.  272-76, s 2387- 2388
• Toussaint, Renaud; Akselvold, Jørgen; Helgesen, Geir; Skjeltorp, Arne Torbjørn & Flekkøy, Eirik Grude (2004). Interaction model for magnetic holes in a ferrofluid layer. Physical Review E. Statistical, Nonlinear, and Soft Matter Physics.  ISSN 1539-3755.  69, s art. no.- 011407
• Vajeeston, Ponniah; Vidya, R.; Ravindran, Ponniah; Fjellvåg, Helmer; Kjekshus, Arne & Skjeltorp, Arne Torbjørn (2002). Electronic structure, phase stability and chemical bonding in Th2Al and Th2AlH4. Physical Review B. Condensed Matter and Materials Physics.  ISSN 1098-0121.  65(075101) Show summary

  We present the results of a theoretical investigation on the electronic structure, bonding nature, and ground-state properties of Th2Al and Th2AlH4 using generalized-gradient-corrected first-principles full-potential density-functional calculations. Th2AlH4 has been reported to violate the "2-Angstrom rule" for H-H separation in hydrides. From Our total-energy as well as force-minimization calculations, we found a shortest H-H separation of 1.95 Angstrom in accordance with recent high-resolution powder neutron-diffraction experiments. When the Th2Al matrix is hydrogenated, the volume expansion is highly anisotropic, which is quite opposite to other hydrides having the same crystal structure. The bonding nature of these materials is analyzed in terms of density of states, crystal-orbital Hamiltonian population, and valence-charge-density analyses. Our calculation predicts a different nature of the bonding between the H atoms along a and c. The strongest bonding in Th2AlH4 is between Th and H along c which form dumbbell-shaped H-Th-H subunits. Due to this strong covalent interaction there is a very small amount of electrons present between the H atoms along c. This reduces the repulsive interaction between the H atoms along c and explains why Th2AlH4 has a shorter H-H separation than most other metal hydrides. The large difference in the interatomic distances between the interstitial regions where one can accommodate H in the ac and ab planes along with the strong covalent interaction between Th and H are the main reasons for highly anisotropic volume expansion on hydrogenation of Th2Al.

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• Skjeltorp, Arne Torbjørn & Belushkin, Alexander V (ed.) (2006). Dynamics of Complex Interconnected Systems: Networks and Bioprocesses. Springer Science+Business Media B.V..  ISBN 978-1-4020-5028-2.  211 s.
• Skjeltorp, Arne Torbjørn & Belushkin, A (ed.) (2004). Forces, Growth and Form in Soft Condensed Matter: At the Interface between Physics and Biology. Kluwer Academic Publishers.  ISBN 1-4020-2339-1.  244 s.

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• Skjeltorp, Arne Torbjørn & Helgesen, Geir (2019). Physics inspired by living matter: dynamics, topology and functionality. The European Physical Journal Special Topics.  ISSN 1951-6355.  227(17), s 2391- 2392 . doi: 10.1140/epjst/e2019-800234-0
• Skjeltorp, Arne Torbjørn & Helgesen, Geir (2016). Editorial. The European Physical Journal Special Topics.  ISSN 1951-6355.  225(4), s 627- 628 . doi: 10.1140/epjst/e2016-60134-1
• Skjeltorp, Arne Torbjørn & Helgesen, Geir (2014). Editorial. The European Physical Journal Special Topics.  ISSN 1951-6355.  223(9), s 1743- 1744 . doi: 10.1140/epjst/e2014-02222-y
• Sobas, Pawel Andrzej; Knudsen, Kenneth; Helgesen, Geir; Skjeltorp, Arne Torbjørn; Mauroy, Henrik & Fossum, Jon Otto (2013). Supercritical CO2 in aerogels and clay materials studied by small angle neutron scattering.
• Sobas, Pawel Andrzej; Knudsen, Kenneth; Helgesen, Geir; Skjeltorp, Arne Torbjørn; Mauroy, Henrik & Fossum, Jon Otto (2013). Supercritical CO2 in aerogels and clay materials studied by small angle neutron scattering.
• Sobas, Pawel Andrzej; Knudsen, Kenneth; Helgesen, Geir; Skjeltorp, Arne Torbjørn; Mauroy, Henrik; Kalantzopoulos, Georgios N. & Fossum, Jon Otto (2013). CO2 adsorption and intercalation in aerogels and clay materials studied by SANS.
• Sobas, Pawel Andrzej; Knudsen, Kenneth; Helgesen, Geir; Skjeltorp, Arne Torbjørn; Måløy, Knut Jørgen; Rozynek, Zbigniew & Fossum, Jon Otto (2013). Dynamic Light Scattering measurements of clay materials in lquid CO2: Preliminary results.
• Sobas, Pawel Andrzej; Knudsen, Kenneth; Helgesen, Geir; Skjeltorp, Arne Torbjørn; Måløy, Knut Jørgen; Rozynek, Zbigniew & Fossum, Jon Otto (2013). Dynamic light scattering measurements of clay materials in liquid CO2: preliminary results.
• Sobas, Pawel Andrzej; Knudsen, Kenneth; Helgesen, Geir; Skjeltorp, Arne Torbjørn; Måløy, Knut Jørgen & Fossum, Jon Otto (2012). Dynamic Light Scattering measurements of clay materials in liquid CO2: Preliminary results.
• Helgesen, Geir; Knudsen, K.D.; Skjeltorp, Arne Torbjørn; Cuesta, H.F.; Elgsæter, A.; Garberg, T.; Næss, S.N. & Knaapila, M. (2009). The Structure of Carbon Cones and Disks.
• Helgesen, Geir; Knudsen, K.D.; Skjeltorp, Arne Torbjørn; Knaapila, M.; Pinheiro, J.P.; Bourgeaux, M.; Heiberg-Andersen, H.; Gunnæs, Anette Eleonora & Prytz, Øystein (2009). The structure and properties of carbon cones.
• Svåsand, Eldrid; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2009). Karbonkjegler og magisk væsker. Fra Fysikkens Verden.  ISSN 0015-9247.  71(2), s 52- 56
• Johansen, Tom Henning; Il'yashenko, E. I. & Skjeltorp, Arne Torbjørn (2008). Method of formation of high gradient magnetic fields and devices for separation of substances.
• Johansen, Tom Henning; Il'yashenko, E. I.; Skjeltorp, Arne Torbjørn & Glebov, V. A. (2008). Method of formation of high gradient magnetic fields and devices for separation of substances.
• Kristiansen, Kai de Lange; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2007). Braid theory and microparticle dynamics in ferrofluids.
• Kristiansen, Kai de Lange; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2006). Matematiske fletter og bibelske vers. Fra Fysikkens Verden.  ISSN 0015-9247.  68(3), s 65- 69
• Kristiansen, Kai de Lange; Svaasand, Eldrid; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2006). Interactions, dynamics and self-assembly of magnetic holes.
• Akselvoll, Jørgen; Skjeltorp, Arne Torbjørn & Helgesen, Geir (2005). Interaction of microparticles dispersed in a ferrofluid.
• Heiberg-Andersen, H.; Helgesen, Geir; Knudsen, K.; Pinheiro, J.P.; Svaasand, E. & Skjeltorp, Arne Torbjørn (2005). Nanocones - a different form of carbon with unique properties.
• Il'yashenko, E. I.; Glebov, V. A.; Glebov, A. V.; Skjeltorp, Arne Torbjørn & Johansen, Tom Henning (2005). Method of Formation of a High Gradient Magnetic Field and a Device for Magnetic Separation.
• Kristiansen, Kai de Lange; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2005). Braided Space-Time Particle Networks.
• Skjeltorp, Arne Torbjørn (2005). Carbon cones – a new form of carbon with exciting properties.
• Skjeltorp, Arne Torbjørn (2005). Nanocarbon.
• Skjeltorp, Arne Torbjørn (2005). Nanoteknologi.
• Skjeltorp, Arne Torbjørn (2005). Properties and applications of nanocarbon.
• Kristiansen, Kai de Lange; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2004). Phenomena in dynamics of magnetic microparticles: Zipf-Mandelbrot relation and anomalous diffusion. Show summary

  The magnetic holes system is a fruitfly model for studying cooperative dynamical processes. By varying the frequency and the anisotropy of the external elliptically polarized magnetic field, a variety of phenomena has been observed and are yet to be explored. Here we present a study of a few-body system giving rise to an intermittent behavior consistent with the Zipf-Mandelbrot relation and the anomalous diffusion. The magnetic holes system is realized by dispersing uniformly sized polystyrene spheres with diameter 50 $\mu$m in a kerosene-based ferrofluid and confined to a 100 $\mu$m thin layer. The external magnetic fields induce an apparent magnetic dipole moment on the microparticles, where all moments have equal strength and direction. The microparticles trace out complicated patterns when subjected to varying external magnetic fields.

• Kristiansen, Kai de Lange; Skjeltorp, Arne Torbjørn & Helgesen, Geir (2004). Complex dynamics and static structures in interconnected particle systems. Show summary

  Soft condensed materials contain many constituents, and can display many surprising and interesting behaviors. This thesis deals with dispersion and sedimentation of particles on micrometer scale in a fluid, which is subjected to external forces. With low concentration of particles, experiments show that the particle motion displays different types of diffusive behavior and that the distribution of their modes is well described by the Zipf-Mandelbrot relation. With high concentration of particles, computer simulation of random packing of a binary mixture of spheres shows many results similar to previous experimental results.

• Skjeltorp, Arne Torbjørn; Akselvold, Jørgen; Christensen, Kai delange; Helgesen, Geir; Toussaint, Renaud & Flekkøy, Eirik Grude (2004). Self assembly and dynamics of magnetic holes.
• Toussaint, Renaud; Akselvoll, Jørgen; Helgesen, Geir; Flekkøy, Eirik Grude & Skjeltorp, Arne Torbjørn (2004). Unexpected results from interactions of magnetic holes in ferrofluid layers.
• Kristiansen, Kai de Lange; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2003). Anomalous Diffusion in Microparticles Dynamics. Show summary

  Based on a magnetic hole system we will demonstrate anomalous diffusion. The magnetic hole system consists of nonmagnetic plastic spheres (voids) on micrometer scale dispersed in a thin layer of ferrofluid. In an external rotating magnetic field, the spheres move due to magnetic dipole-dipole interactions. Their motions in the plan are captured in real time by a video camera on a light microscope. Introducing the time axis together with the planar axis we find their trajectories in space-time. With several spheres (e.g. 7) we observe a braided structure of the trajectories. Applying braid theory we can extract the essential information about the dynamics. A useful quantity is the topological invariant writhe. For motions where the step sizes is described by a Gaussian distribution, the variance of the position as a function of time is proportional to the time. This type of behavior is most common in Nature, but there are motions which deviate from this, and give rise to power law dependence of the variance with an exponent different from 1, called anomalous diffusion. We will show that anomalous diffusion can be observed in our simple colloidal system.

• Kristiansen, Kai de Lange; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2003). Braid theory and Zipf relation used in dynamics of magnetic microparticles. Show summary

  We have studied the dynamics of a few body system of microparticles using rank-ordering statistics. This dynamical system was made up of micrometer sized polystyrene spheres dispersed in a thin layer of ferrofluid, forming so called magnetic holes. The motion of microspheres were driven by external magnetic fields and the induced magnetic dipole-dipole interaction. The world lines from the magnetic holes are captures using a video camera and an optical microscope. The dynamical modes were described in terms of positive permutation braids, a notation from mathematical braid theory. Rank-ordering statistics on these permutation braids showed a power law consistent with the so called Zipf relation. The time-lag auto-correlation function of the positive permutation braids showed only short range correlation in time. A simple numerical simulation of the experimental system was also performed and showed similar results.

• Toussaint, Renaud; Helgesen, Geir; Flekkøy, Eirik Grude; Akselvoll, Jørgen & Skjeltorp, Arne Torbjørn (2003). Magnetic holes population in ferrofluids: interactions, phase diagram and fluctuations scaling.
• Toussaint, Renaud; Helgesen, Geir; Flekkøy, Eirik Grude; Akselvoll, Jørgen & Skjeltorp, Arne Torbjørn (2003). Magnetic holes populations in ferrofluids: interactions and phases.
• Toussaint, Renaud; Akselvoll, Jørgen; Flekkøy, Eirik Grude; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2002). Magnetic holes in ferrofluid layers: interactions, phases and brownian motion.
• Kristiansen, Kai de Lange; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2002). Zipf Relation and Braid Theory used in Microparticle Dynamics. Show summary

  We have tried to analyse the dynamical modes in a physical system using rank-ordering statistics. In an intermittent range in the system the statistics shows a behavior consistent with Zipf relation. This type of behavior were first described by G.K. Zipf and is a relation between probabilities P(r) of occurrence of an element and its rank r given by: P(r) \sim r^(-gamma), where gamma is a parameter, usually gamma \approx 1. The rank labels the element that occurs most frequently by 1, second most frequently by 2 etc. In the physical system under study we looked on the occurrences of the different dynamical modes. Our physical system under study contains plastic spheres of micrometer size dispersed in a magnetic fluid. These spheres are driven by an external, rotating, elliptically polarized magnetic field. The dynamics of the spheres are analysed by use of braid mathematics. Then different dynamical modes correspond to braid permutations. When we use rank-ordering statistics on the system in some parameter range of the magnetic field, we find behavior in agreement with Zipf relation with gamma near 1.

• Toussaint, Renaud; Akselvoll, Jørgen; Flekkøy, Eirik Grude; Helgesen, Geir & Skjeltorp, Arne Torbjørn (2001). Magnetic holes populations in ferrofluids: interactions, phase diagram, chain-roughening and applications.
• Vajeeston, Ponniah; Ravindran, Ponniah; Vidya, R.; Fjellvåg, Helmer; Kjekshus, Arne & Skjeltorp, Arne Torbjørn (2001). Theoretical investigation of hydrides based on Cu2Al-type materials.

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