Publications – Bo Jakobsen

Journal papers

D. B. Noirat, B. Frick, B. Jakobsen, M. Appel, and K. Niss. Density scaling and isodynes in glycerol-water mixtures. Phys. Chem. Chem. Phys., 26:29003–29014, 2024. [ DOI ] This paper presents dielectric and neutron spectroscopy data on two different glycerol-water mixtures at elevated pressures. Glycerol-water liquid mixtures have a high concentration of hydrogen bonds which usually is expected to lead to complex dynamics. However, with regard to the pressure dependence of the dynamics we reveal a surprisingly simple picture. Different aspects of the dynamics have the same pressure dependence, in other words the phase diagram of the liquids have so-called isodynes, density scaling is also observed to hold reasonably well and there is even some reminiscence of isochronal superposition. This suggests that these aspect of liquid dynamics are very general and hold for different types of intermolecular interactions.

S. Ariaee, B. Jakobsen, P. Norby, D.-M. Smilgies, K. Almdal, and D. Posselt. Thin film and bulk morphology of pi-ps-pmma miktoarm star terpolymers with both weakly and strongly segregated arm pairs. Polymer, 283:126202, 2023. [ DOI ]

S. Ariaee, B. Jakobsen, I. Pedersen, T. Rasmussen, and D. Posselt. Solvothermal vapor annealing setup for thin film treatment: A compact design with in situ solvent vapor concentration probe. AIP Advances, 13:065226, 2023. [ DOI ]

M. Mikkelsen, K. Eliasen, N. Lindemann, K. Moch, R. Böhmer, A. Karimi, J. Lacayo-Pineda, B. Jakobsen, K. Niss, T. Christensen, and T. Hecksher. Piezoelectric shear rheometry: Further developments in experimental implementation and data extraction. Journal of Rheology, 66:983–1003, 2022. [ DOI ]

T. Freiesleben, K. Thomsen, A. Murray, R. Sohbati, M. Jain, S. Hvidt, B. Jakobsen, and T. Aubry. Rock surface and sand-sized sediment quartz dating using optically stimulated luminescence of a middle-to-upper palaeolithic sequence at the bordes-fitte rock shelter (les roches d'abilly, central france). Quaternary Geochronology, 73:101406, November 2022. [ DOI ]

B. Jakobsen, A. T. Holmes, T. Rasmussen, H. Schneider, A. Pettersson, A. Hiess, and K. Niss. Huginn: A peltier-based sub-cryostat for neutron scattering. Journal of Neutron Research, 21:47–57, 2019. [ DOI ]

A. Sanz, H. W. Hansen, B. Jakobsen, I. H. Pedersen, S. Capaccioli, K. Adrjanowicz, M. Paluch, J. Gonthier, B. Frick, E. Lelièvre-Berna, J. Peters, and K. Niss. High-pressure cell for simultaneous dielectric and neutron spectroscopy. Review of Scientific Instruments, 89(2):023904, 2018. [ DOI ]

J. Neuefeind, A. L. Skov, J. E. Daniels, V. Honkimäki, B. Jakobsen, J. Oddershede, and H. F. Poulsen. A multiple length scale description of the mechanism of elastomer stretching. RSC Advances, 6:95910–95919, 2016. [ DOI ] Conventionally, the stretching of rubber is modeled exclusively by rotations of segments of the embedded polymer chains; i.e. changes in entropy. However models have not been tested on all relevant length scales due to a lack of appropriate probes. Here we present a universal X-ray based method for providing data on the structure of rubbers in the 2–50 Å range. First results relate to the elongation of a silicone rubber. We identify several non-entropic contributions to the free energy and describe the associated structural changes. By far the largest contribution comes from structural changes within the individual monomers, but among the contributions is also an elastic strain, acting between chains, which is 3--4 orders of magnitude smaller than the macroscopic strain, and of the opposite sign, i.e. extension of polymer chains in the direction perpendicular to the stretch. This may be due to trapped entanglements relaxing to positions close to the covalent crosslinks.

B. Jakobsen, A. Sanz, K. Niss, T. Hecksher, I. H. Pedersen, T. Rasmussen, T. Christensen, N. B. Olsen, and J. C. Dyre. Thermalization calorimetry: A simple method for investigating glass transition and crystallization of supercooled liquids. AIP Advances, 6:055019, 2016. [ DOI ] We present a simple method for fast and cheap thermal analysis on supercooled glass-forming liquids. This “Thermalization Calorimetry” technique is based on monitoring the temperature and its rate of change during heating or cooling of a sample for which the thermal power input comes from heat conduction through an insulating material, i.e., is proportional to the temperature difference between sample and surroundings. The monitored signal reflects the sample's specific heat and is sensitive to exo- and endothermic processes. The technique is useful for studying supercooled liquids and their crystallization, e.g., for locating the glass transition and melting point(s), as well as for investigating the stability against crystallization and estimating the relative change in specific heat between the solid and liquid phases at the glass transition.

L. A. Roed, K. Niss, and B. Jakobsen. High pressure specific heat spectroscopy reveals simple relaxation behavior of glass forming molecular liquid. The Journal of Chemical Physics - Communication, 143:221101, 2015. [ DOI ] The frequency dependent specific heat has been measured under pressure for the molecular glass forming liquid 5-polyphenyl-4-ether in the viscous regime close to the glass transition. The temperature and pressure dependences of the characteristic time scale associated with the specific heat is comed to the equivalent time scale from dielectric spectroscopy performed under identical conditions. It is shown that the ratio between the two time scales is independent of both temperature and pressure. This observation is non-trivial and demonstrates the existence of specially simple molecular liquids in which different physical relaxation processes are both as function of temperature and pressure/density governed by the same underlying "inner clock." Furthermore, the results are discussed in terms of the recent conjecture that van der Waals liquids, like the measuredliquid, comply to the isomorph theory.

K. Adrjanowicz, B. Jakobsen, T. Hecksher, K. Kaminski, M. Dulski, M. Paluch, and K. Niss. Communication: Slow supramolecular mode in amine and thiol derivatives of 2-ethyl-1-hexanol revealed by combined dielectric and shear-mechanical studies. The Journal of Chemical Physics - Communication, 143(18):181102, 2015. [ DOI ] In this paper, we present results of dielectric and shear-mechanical studies for amine (2-ethyl-1-hexylamine) and thiol (2-ethyl-1-hexanethiol) derivatives of the monohydroxy alcohol, 2-ethyl-1-hexanol. The amine and thiol can form hydrogen bonds weaker in strength than those of the alcohol. The combination of dielectric and shear-mechanical data enables us to reveal the presence of a relaxation mode slower than the alpha-relaxation. This mode is analogous to the Debye mode seen in monohydroxy alcohols and demonstrates that supramolecular structures are present for systems with lower hydrogen bonding strength. We report some key features accompanying the decrease in the strength of the hydrogen bonding interactions on the relaxationdynamics close to the glass-transition. This includes changes (i) in the amplitude of the Debye and alpha-relaxations and (ii) the seation between primary and secondary modes.

T. Freiesleben, R. Sohbati, A. Murray, M. Jain, S. al Khasawneh, S. Hvidt, and B. Jakobsen. Mathematical model quantifies multiple daylight exposure and burial events for rock surfaces using luminescence dating. Radiation Measurements, 81, 2015. [ DOI ]

T. Hecksher and B. Jakobsen. Supramolecular structures in monohydroxy alcohols: Insights from shear-mechanical studies of a systematic series of octanol structural isomers. Journal of Chemical Physics - Communication, 141:101104, 2014. [ DOI ] A recent study [C. Gainaru, R. Figuli, T. Hecksher, B. Jakobsen, J. C. Dyre, M. Wilhelm, and R. Böhmer, Phys. Rev. Lett. 112, 098301 (2014)] of two supercooled monohydroxy alcohols close to the glass-transition temperature showed that the Debye peak, thus far mainly observed in the electrical response, also has a mechanical signature. In this work, we apply broadband shear-mechanical spectroscopy to a systematic series of octanol structural isomers, x-methyl-3-heptanol (with x ranging from 2 to 6).We find that the characteristics of the mechanical signature overall follow the systematic behavior observed in dielectric spectroscopy. However, the influence from the molecular structure is strikingly small in mechanics (comed to roughly a factor 100 increase in dielectric strength) and one isomer clearly does not conform to the general ordering. Finally, the mechanical data surprisingly indicate that the size of the supramolecular structures responsible for the Debye process is nearly unchanged in the series.

C. Gainaru, M. Wikarek, S. Pawlus, M. Paluch, R. Figuli, M. Wilhelm, T. Hecksher, B. Jakobsen, J. C. Dyre, and R. Böhmer. Oscillatory shear and high-pressure dielectric study of 5-methyl-3-heptanol. Colloid and Polymer Science, 292:1913–1921, 2014. Special Issue in honor of Prof. Dr. Friedrich Kremer on the occasion of his 65th birthday. [ DOI ] The monohydroxy alcohol 5-methyl-3-heptanol is studied using rheology at ambient pressure and using dielectric spectroscopy at elevated pressures up to 1.03 GPa. Both experimental techniques reveal that the relaxational behavior of this liquid is intermediate between those that show a large Debye process, such as 2-ethyl-1-hexanol, or a small Debye-like feature, such as 4-methyl-3-heptanol, with which comisons are made. Various phenomenological approaches assigning a time scale for the rheological signature of supramolecular dynamics in monohydroxy alcohols are discussed.

C. Gainaru, R. Figuli, T. Hecksher, B. Jakobsen, J. C. Dyre, M. Wilhelm, and R. Böhmer. Shear-modulus investigations of monohydroxy alcohols: Evidence for a short-chain-polymer rheological response. Physical Review Letters, 112:098301, 2014. [ DOI ] Liquids composed of small-molecule monohydroxy alcohols are demonstrated to display rheological behavior typical for oligomeric chains. This observation was made possible by rheological experiments in which more than seven decades in frequency and more than five decades on the mechanical modulus scale are covered. The singly hydrogen-bonded monohydroxy alcohols were chosen because they display significant, but surprisingly poorly understood effects of intermolecular association. Based on the present shear study, one can apply theoretical concepts of polymer science to understand the anomalous physical behavior of a wide range of hydrogen-bonded liquids.

B. Jakobsen, T. Hecksher, T. Christensen, N. B. Olsen, J. C. Dyre, and K. Niss. Identical temperature dependence of the time scales of several linear-response functions of two glass-forming liquids. Journal of Chemical Physics - Communication, 136:081102, 2012. [ DOI ] The frequency-dependent dielectric constant, shear and adiabatic bulk moduli, longitudinal thermal expansion coefficient, and longitudinal specific heat have been measured for two van der Waals glass-forming liquids, tetramethyl-tetraphenyl-trisiloxane (DC704) and 5-polyphenyl-4-ether. Within the experimental uncertainties the loss-peak frequencies of the measured response functions have identical temperature dependence over a range of temperatures, for which the Maxwell relaxation time varies more than nine orders of magnitude. The time scales are ordered from fastest to slowest as follows: Shear modulus, adiabatic bulk modulus, dielectric constant, longitudinal thermal expansion coefficient, and longitudinal specific heat. The ordering is discussed in light of the recent conjecture that van der Waals liquids are strongly correlating, i.e., approximate single-ameter liquids.

U. Lienert, S. Li, C. Hefferan, J. Lind, R. Suter, J. Bernier, N. Barton, M. Brandes, M. Mills, M. Miller, B. Jakobsen, and W. Pantleon. High-energy diffraction microscopy at the advanced photon source. JOM, 63:70–77, 2011.

D. Gundermann, U. R. Pedersen, T. Hecksher, N. P. Bailey, B. Jakobsen, T. Christensen, N. B. Olsen, T. B. Schrøder, D. Fragiadakis, R. Casalini, C. M. Roland, J. C. Dyre, and K. Niss. Predicting the density scaling exponent from prigogine-defay ratio measurements. Nature Physics, 7:816–821, 2011. [ DOI ] Understanding the origin of the dramatic temperature and density dependence of the relaxation time of glass-forming liquids is a fundamental challenge in glass science. The recently established "density-scaling" relation quantifies the relative importance of temperature and density for the relaxation time in terms of a material-dependent exponent. We show that this exponent for approximate single-ameter liquids can be calculated from thermoviscoelastic linear-response data at a single state point, for instance an ambient-pressure state point. This prediction is confirmed for the van der Waals liquid tetramethyl-tetraphenyl-trisiloxane. Consistent with this, a compilation of literature data for the Prigogine-Defay ratio shows that van derWaals liquids and polymers are approximate single-ameter systems, whereas associated and network-forming liquids are not.

T. Christensen, B. Jakobsen, J. Papini, T. Hecksher, J. C. Dyre, and N. B. Olsen. A combined measurement of thermal and mechanical relaxation. Journal of Non-Crystalline Solids, 357:346–350, 2011. “6th IDMRCS” special issue. [ DOI ] In order to describe relaxation the thermodynamic coefficient (1)/(β_s)=(( V)/(S) )_p can be generalized into a complex frequency-dependent cross response function. We explore theoretically the possibility of measuring (1)/(β_S) for a supercooled liquid near the glass transition. This is done by placing a thermistor in the middle of the liquid which itself is contained in a spherical piezoelectric shell. The piezoelectric voltage response to a thermal power generated in the thermistor is found to be proportional to (1)/(β_S) but factors pertaining to heat diffusion and adiabatic compressibility κ_S(ω) do also intervene. Weestimate a measurable piezoelectric voltage of 1 mV to be generated at 1 Hz for a heating power of 0.3mW. Together with κ_S(ω) and the longitudinal specific heat c_l(ω) which may also be found in the same setup a complete triple of thermoviscoelastic response functions may be determined when supplemented with shear modulus data.

B. Jakobsen, K. Niss, C. Maggi, N. B. Olsen, T. Christensen, and J. C. Dyre. Beta relaxation in the shear mechanics of viscous liquids: Phenomenology and network modeling of the alpha-beta merging region. Journal of Non-Crystalline Solids, 357:267–273, 2011. “6th IDMRCS” special issue. [ DOI ] The phenomenology of the beta relaxation process in the shear-mechanical response of glass-forming liquids is summarized and comed to that of the dielectric beta process. Furthermore, we discuss how to model the observations by means of standard viscoelastic modeling elements. Necessary physical requirements to such a model are outlined, and it is argued that physically relevant models must be additive in the shear compliance of the alpha and beta ts. A model based on these considerations is proposed and fitted to data for Polyisobutylene 680.

B. Jakobsen, N. B. Olsen, and T. Christensen. Frequency-dependent specific heat from thermal effusion in spherical geometry. Physical Review E, 81:061505, 2010. [ DOI ] We present a method of measuring the frequency-dependent specific heat at the glass transition applied to 5-polyphenyl-4-ether. The method employs thermal waves effusing radially out from the surface of a spherical thermistor that acts as both a heat generator and a thermometer. It is a merit of the method comed to planar effusion methods that the influence of the mechanical boundary conditions is analytically known. This implies that it is the longitudinal rather than the isobaric specific heat that is measured. As another merit the thermal conductivity and specific heat can be found independently. The method has highest sensitivity at a frequency where the thermal diffusion length is comable to the radius of the heat generator. This limits in practice the frequency range to 2–3 decades. An account of the 3ω technique used including higher-order terms in the temperature dependence of the thermistor and in the power generated is furthermore given.

C. Maggi, B. Jakobsen, and J. C. Dyre. Unique dynamic correlation length in supercooled liquids. arXiv:1003.0341v1 [cond-mat.soft], 2010. [ http ]

W. Pantleon, C. Wejdemann, B. Jakobsen, U. Lienert, and H. Poulsen. Evolution of deformation structures under varying loading conditions followed in situ by high angular resolution 3dxrd. Materials Science and Engineering A, 524:55–63, 2009. [ DOI ] With high angular resolution three-dimensional X-ray diffraction, individual subgrains are traced in the bulk of a polycrystalline specimen and their dynamics is followed in situ during varying loading conditions. The intensity distribution of single Bragg reflections from an individual grain is analyzed in reciprocal space. It consists of sharp high-intensity peaks arising from subgrains superimposed on a cloud of lower intensity arising from dislocationwalls. Individual subgrains can be distinguished by their unique combination of orientation and elastic strain. The responses of polycrystalline copper to different loading conditions are presented: during uninterrupted tensile deformation, formation of subgrains can be observed concurrently with broadening of the Bragg reflection shortly after onset of plastic deformation. With continued tensile deformation, the subgrain structure develops intermittently. When the traction is terminated, stress relaxation occurs and number, size and orientation of subgrains are found to be constant. The subgrain structure freezes and only a minor clean-up of the dislocation structure is observed. When changing the tensile direction after pre-deformation in tension, a systematic correlation between the degree of strain path change and the changes in the dislocation structure quantified by the volume fraction of the subgrains is established. For obtaining the subgrain volume fraction, a new fitting method has been developed for titioning the contributions of subgrains and dislocation walls.

A. I. Nielsen, T. Christensen, B. Jakobsen, K. Niss, N. B. Olsen, R. Richert, and J. C. Dyre. Prevalence of approximate sqrt(t) relaxation for the dielectric α process in viscous organic liquids. Journal of Chemical Physics, 130:154508, 2009. [ DOI ] This paper presents dielectric relaxation data for organic glass-forming liquids compiled from different groups and supplemented by new measurements. The main quantity of interest is the “minimum slope” of the α dielectric loss plotted as a function of frequency in a log-log plot, i.e., the numerically largest slope above the loss peak frequency. The data consisting of 347 spectra for 53 liquids show prevalence of minimum slopes close to -1/2, corresponding to approximate t dependence of the dielectric relaxation function at short times. The paper studies possible correlations between minimum slopes and (1) temperature quantified via the loss peak frequency; (2) how well an inverse power-law fits data above the loss peak; (3) degree of time-temperature superposition; (4) loss peak half width; (5) deviation from non-Arrhenius behavior; (6) loss strength. For the first three points we find correlations that show a special status of liquids with minimum slopes close to -1/2. For the last three points only fairly insignificant correlations are found, with the exception of large-loss liquids that have minimum slopes that are numerically significantly larger than 1/2. We conclude that –- excluding large-loss liquids –- approximate sqrt(t) relaxation appears to be a generic property of the relaxation of organic glass formers.

B. Jakobsen, H. F. Poulsen, U. Lienert, J. Bernier, C. Gundlach, and W. Pantleon. Stability of dislocation structures in copper towards stress relaxation investigated by high angular resolution 3d x-ray diffraction. Physica Status Solidi (a), 206:21–30, 2009. [ DOI ] A 300μm thick tensile specimen of OFHC copper is subjected to a tensile loading sequence and deformed to a maximal strain of 3.11%. Using the novel three-dimensional X-ray diffraction method “High angular resolution 3DXRD”, the evolution of the microstructure within a deeply embedded grain is characterised in-situ by the behaviour of individual subgrains. The loading sequence consists of three continuous deformation stages with strain rates of 1.1×10^-6s^-1 and 3×10^-2s^-1, in each case followed by a period of extended stress relaxation at fixed motor positions, as well as an unloading step. In contrast to the deformation stages, during each stress relaxation stage, number, size and orientation of subgrains are found to be constant, while a minor amount of clean-up of the microstructure is observed as narrowing of the radial X-ray diffraction line profile. The associated decrease in the width of the strain distribution indicates homogenization of the elastic strains present in the deformation structure. During reloading, the subgrain structure seemingly starts to develop further when the entire dislocation structure is deforming plastically. Upon unloading of the sample, the average backward strain of the subgrains increases.

C. Maggi, B. Jakobsen, T. Christensen, N. B. Olsen, and J. C. Dyre. Supercooled liquid dynamics studied via shear-mechanical spectroscopy. The Journal of Physical Chemistry B, 112:16320–16325, 2008. [ DOI | http ] We report dynamical shear-modulus measurements for five glass-forming liquids (pentaphenyltrimethyltrisiloxane, diethyl phthalate, dibutyl phthalate, 1,2-propanediol, and m-touluidine). The shear-mechanical spectra are obtained by the piezoelectric shear-modulus gauge (PSG) method. This technique allows one to measure the shear modulus (10⁵–10¹⁰ Pa) of the liquid within a frequency range from 1 mHz to 10 kHz. We analyze the frequency-dependent response functions to investigate whether time-temperature superposition (TTS) is obeyed. We also study the shear-modulus loss-peak position and its high-frequency t. It has been suggested that when TTS applies, the high-frequency side of the imaginary t of the dielectric response decreases like a power law of the frequency with an exponent -1/2. This conjecture is analyzed on the basis of the shear mechanical data. We find that TTS is obeyed for pentaphenyltrimethyltrisiloxane and in 1,2-propanediol while in the remaining liquids evidence of a mechanical β process is found. Although the high-frequency power law behavior ω^-α of the shear loss may approach a limiting value of α= 0.5 when lowering the temperature, we find that the exponent lies systematically above this value (around 0.4). For the two liquids without β relaxation (pentaphenyltrimethyltrisiloxane and 1,2-propanediol) we also test the shoving model prediction, according to which the relaxation time activation energy is proportional to the instantaneous shear modulus. We find that the data are well described by this model.

B. Jakobsen, C. Maggi, T. Christensen, and J. C. Dyre. Investigation of the shear-mechanical and dielectric relaxation processes in two monoalcohols close to the glass transition. Journal of Chemical Physics, 129:184502, 2008. [ DOI | http ] Shear-mechanical and dielectric measurements on the two monohydroxy (monoalcohol) molecular glass formers 2-ethyl-1-hexanol and 2-butanol close to the glass-transition temperature are presented. The shear-mechanical data are obtained using the piezoelectric shear-modulus gauge method covering frequencies from 1 mHz to 10 kHz. The shear-mechanical relaxation spectra show two processes, which follow the typical scenario of a structural (alpha) relaxation and an additional (Johari-Goldstein) beta relaxation. The dielectric relaxation spectra are dominated by a Debye-type peak with an additional non-Debye peak visible. This Debye-type relaxation is a common feature peculiar to monoalcohols. The time scale of the non-Debye dielectric relaxation process is shown to correspond to the mechanical structural (alpha) relaxation. Glass-transition temperatures and fragilities are reported based on the mechanical alpha relaxation and the dielectric Debye-type process, showing that the two glass-transition temperatures differ by approximately 10 K and that the fragility based on the Debye-type process is a factor of 2 smaller than the structural fragility. If a mechanical signature of the Debye-type relaxation exists in these liquids, its relaxation strength is at most 1% and 3% of the full relaxation strength of 2-butanol and 2-ethyl-1-hexanol, respectively. These findings support the notion that it is the non-Debye dielectric relaxation process that corresponds to the structural alpha relaxation in the liquid.

N. P. Bailey, T. Christensen, B. Jakobsen, K. Niss, N. B. Olsen, U. R. Pedersen, T. B. Schrøder, and J. C. Dyre. Glass-forming liquids: one or more 'order' ameters? Journal of Physics: Condensed Matter, 20:244113, 2008. [ DOI ] We first summarize the classical arguments that the vast majority of glass-forming liquids require more than one 'order' ameter for their description. Critiques against this conventional wisdom are then presented, and it is argued that the matter deserves to be reconsidered in the light of recent experimental developments. Out of the eight basic thermoviscoelastic frequency-dependent response functions, there are generally three independent functions. For stochastic dynamics we show that there are only two independent response functions; for this case it is shown how analytic continuation may be utilized to express the third response functions in terms of two others. Operational criteria are presented for the linear thermoviscoelasticity being described by a single 'order' ameter, in which case there is just one independent thermoviscoelastic response function. It is shown that a description with a single 'order' ameter applies to a good approximation whenever thermal equilibrium fluctuations of fundamental variables like energy and pressure are strongly correlated. Results from computer simulations showing that this is the case for a number of simple glass-forming liquids, as well as a few exceptions, are briefly presented. Finally, we briefly discuss a new conjecture according to which experiments at varying temperature and pressure follow the density scaling expression for the relaxation time, τ= F(ρ^x/T) (ρ and T are density and temperature), if and only if the liquid is 'strongly correlating', i.e., to a good approximation is described by a single 'order' ameter.

B. Jakobsen, U. Lienert, J. Almer, H. Poulsen, and W. Pantleon. Direct observation of strain in bulk subgrains and dislocation walls by high angular resolution three-dimensional X-ray diffraction. Materials Science and Engineering: A, 483–484:641--643, 2008. Proceedings of ICSMA14. [ DOI ] The X-ray diffraction method “High Angular Resolution 3DXRD” is briefly introduced, and results are presented for a single bulk grain in a polycrystalline copper sample deformed in tension. It is found that the 3D reciprocal space intensity distribution of a 400 reflection associated with the grain, shows a distinct structure consisting of sharp bright peaks superimposed on a cloud of enhanced intensity. The bright peaks (which arise from individual subgrains) are found to be subjected to backward strain (on average) while the fraction of the material giving rise to the cloud of enhanced intensity is subjected to forward strain. Based on the latter observation the, originally tentative, interpretation of the cloud as arising from dislocation walls is substantiated.

M. Brøns, B. Jakobsen, K. Niss, A. Bisgaard, and L. K. Voigt. Streamline topology in the near wake of a circular cylinder at moderate Reynolds numbers. Journal of Fluid Mechanics, 584:23–43, 2007. [ DOI ] For the flow around a circular cylinder, the steady flow changes its topology at a Reynolds number around 6 where the flow seates and a symmetric double separation zone is created. At the bifurcation point, the flow topology is locally degenerate, and by a bifurcation analysis we find all possible streamline patterns which can occur as perturbations of this flow. We show that there is no a priori topological limitation from further assuming that the flow fulfils the steady Navier-Stokes equations or from assuming that a Hopf bifurcation occurs close to the degenerate flow. The steady flow around a circular cylinder experiences a Hopf bifurcation for a Reynolds number about 45–-49. Assuming that this Reynolds number is so close to the value where the steady seation occurs that the flow here can be considered a perturbation of the degenerate flow, the topological bifurcation diagram will contain all possible instantaneous streamline patterns in the periodic regime right after the Hopf bifurcation. On the basis of the spatial and temporal symmetry associated with the circular cylinder and the structure of the topological bifurcation diagram, two periodic scenarios of instantaneous streamline patterns are conjectured. We confirm numerically the existence of these scenarios, and find that the first scenario exists only in a narrow range after the Hopf bifurcation whereas the second one persists through the entire range of Re where the flow can be considered two-dimensional. Our results corroborate previous experimental and computational results.

B. Jakobsen, H. F. Poulsen, U. Lienert, and W. Pantleon. Direct determination of elastic strains and dislocation densities in individual subgrains in deformation structures. Acta Materialia, 55:3421–3430, 2007. [ DOI ] A novel synchrotron-based technique “High angular resolution 3DXRD” is presented in detail, and applied to the characterization of OFHC copper at a tensile deformation of 2%. The position and shape in reciprocal space of 14 peaks originating from deeply-embedded individual subgrains is reported. From this dataset the density of redundant dislocations in the individual subgrains is inferred to be below 12·10¹²m^-2 on average. It is found that the subgrains on average experience a reduction in strain of 0.9·10^-4 with respect to the mean elastic strain of the full grain, a rather wide distribution of the strain difference between the subgrains (twice the standard deviation is 2.9·10^-4), and a narrow internal strain distribution (upper limit is 2.4·10^-4 full width at half maximum).

B. Jakobsen, H. F. Poulsen, U. Lienert, X. Huang, and W. Pantleon. Investigation of the deformation structure in an aluminium magnesium alloy by high angular resolution three-dimensional X-ray diffraction. Scripta Materialia, 56:769–772, 2007. [ DOI ] The deformation structure in individual grains of an aluminium magnesium alloy deformed up to 10% in tension is characterized with high angular resolution three-dimensional X-ray diffraction. The three-dimensional intensity distribution (in reciprocal space) of all reflections investigated is rather smooth. The absence of individual sharp peaks indicates the absence of a dislocation cell structure, which was confirmed by transmission electron microscopy. Nevertheless, the formation of different orientation components associated with different elastic strains is evident within a grain.

B. Jakobsen, H. F. Poulsen, U. Lienert, J. Almer, S. D. Shastri, H. O. Sørensen, C. Gundlach, and W. Pantleon. Formation and subdivision of deformation structures. Science, 312:889–892, 2006. [ DOI | http ] During plastic deformation of metals and alloys dislocations arrange in ordered patterns. How and when these self-organization processes take place has remained elusive, as in situ observations have not been feasible. Here we present an X-ray diffraction method, providing data on the dynamics of individual, deeply embedded dislocation structures. First results relate to the tensile deformation of pure copper. Structural elements with a size of 1 μm are found to form during deformation already at 0.4% strain. Unexpectedly, the dislocation-free regions show intermittent dynamics, e.g. appearing and disappearing with proceeding deformation, even displaying transient splitting behaviour. Insight into these processes is vital for optimizing the strength and mechanical performance of deformed materials as well as an understanding of work-hardening.

H. Sørensen, B. Jakobsen, E. Knudsen, E. Lauridsen, S. Nielsen, H. Poulsen, S. Schmidt, G. Winther, and L. Margulies. Mapping grains and their dynamics in three dimensions. Nuclear Instruments and Methods in Physics Research Section B, 246:232–237, 2006. [ DOI ] The three-dimensional X-ray diffraction (3DXRD) microscope has become a mature tool to investigate the microstructure in the bulk of polycrystalline materials. The present paper describes the 3DXRD method together with two applications. The first application presented is a study of grain rotations during plastic tensile deformation of polycrystalline aluminium. The second is the acquisition of a video revealing the 3D growth of an embedded nuclei during recrystallization of a deformed aluminium sample.

K. Niss, B. Jakobsen, and N. B. Olsen. Dielectric and shear mechanical relaxations in glass-forming liquids: A test of the Gemant-DiMarzio-Bishop model. Journal of Chemical Physics, 123:234510, 2005. [ DOI | http ] The Gemant-DiMarzio-Bishop model, which connects the frequency-dependent shear modulus to the frequency-dependent dielectric constant, is reviewed and a new consistent macroscopic formulation is derived. It is moreover shown that this version of the model can be tested without fitting ameters. The reformulated version of the model is analyzed and experimentally tested. It is demonstrated that the model has several nontrivial qualitative predictions: the existence of an elastic contribution to the high-frequency limit of the dielectric constant, a shift of the shear modulus loss peak frequency to higher frequencies comed with the loss peak frequency of the dielectric constant, a broader alpha peak, and a more pronounced beta peak in the shear modulus when comed with the dielectric constant. It is shown that these predictions generally agree with experimental findings and it is therefore suggested that the Gemant-DiMarzio-Bishop model is correct on a qualitative level. The quantitative agreement between the model and the data is on the other hand moderate to poor. It is discussed if a model-free comison between the dielectric and shear mechanical relaxations is relevant, and it is concluded that the shear modulus should be comed with the rotational dielectric modulus, 1/(ε(ω)-n²), which is extracted from the Gemant-DiMarzio-Bishop model, rather than to the dielectric susceptibility or the conventional dielectric modulus M=1/ε(ω).

B. Jakobsen, K. Niss, and N. B. Olsen. Dielectric and shear mechanical alpha and beta relaxations in seven glass-forming liquids. Journal of Chemical Physics, 123:234511, 2005. [ DOI | http ] We present shear mechanical and dielectric measurements taken on seven liquids: triphenylethylene, tetramethyltetra-phenyltrisiloxane Dow Corning 704® diffusion pump fluid, polyphenyl ether Santovac® 5 vacuum pump fluid, perhydrosqualene, polybutadiene, decahydroisoquinoline DHIQ, and tripropylene glycol. The shear mechanical and dielectric measurements are for each liquid performed under identical thermal conditions close to the glass transition temperature. The liquids span four orders of magnitude in dielectric relaxation strength and include liquids with and without Johari-Goldstein beta relaxation. The shear mechanical data are obtained by the piezoelectric shear modulus gauge method giving a large frequency span 10^-3-10^4.5 Hz. This allows us to resolve the shear mechanical Johari-Goldstein beta peak in the equilibrium DHIQ liquid. We moreover report a signature a pronounced rise in the shear mechanical loss at frequencies above the alpha relaxation of a Johari-Goldstein beta relaxation in the shear mechanical spectra for all the liquids which show a beta relaxation in the dielectric spectrum. It is found that both the alpha and beta loss peaks are shifted to higher frequencies in the shear mechanical spectrum comed to the dielectric spectrum. It is in both the shear and dielectric responses found that liquids obeying time-temperature superposition also have a high-frequency power law with exponent close to -1/2. It is moreover seen that the less temperature dependent the spectral shape is, the closer it is to the universal -1/2 power-law behavior. The deviation from this universal power-law behavior and the temperature dependencies of the spectral shape are rationalized as coming from interactions between the alpha and beta relaxations.

Software

B. Jakobsen, T. Hecksher, and T. E. Christensen. RUSC (Roskilde University Shear Code) (v 1.0). Zenodo, 2024. [ DOI ] RUSC (Roskilde University Shear Code) is analysis software for calculating the frequency-dependent complex shear modulus from capacitance measurements on a piezoelectric shear gauge (PSG). The piezoelectric shear rheometry technique, the PSG devices, and the RUSC software have been developed over many years in the "Glass and Time" physics group at Roskilde University.

Book chapters

W. Pantleon, C. Wejdemann, B. Jakobsen, H. F. Poulsen, and U. Lienert. Strains and dislocation gradients from diffraction, chapter High Resolution Reciprocal Space Mapping for Characterizing Deformation Structures. Imperial College Press (World Scientific Publishing), 2014. [ http ]

Reports

B. Jakobsen, T. S. Rasmussen, and K. Niss. Huginn Sub-cryostat Documentation, RUC/ESS HUGINN project, Work Unit 2b. Technical report, October 2017.

B. Jakobsen and K. Niss. Huginn SANS “multi-temperature cuvette holder” documentation, RUC/ESS HUGINN project, Work Units 2b and 3b. Technical report, October 2017.

B. Jakobsen, T. S. Rasmussen, and K. Niss. “Huginn Peltier Driver Documentation”, RUC/ESS HUGINN project, Work Units 2b and 3b. Technical report, September 2017.

B. Jakobsen and K. Niss. “Huginn Sub-cryostat Software Documentation”, RUC/ESS HUGINN project, Work Unit 2b. Technical report, October 2017.

B. Jakobsen and K. Niss. “peltier element based sub-cryostat” Design report, RUC/ESS HUGINN project, Work Unit 2a. Technical report, February 2017.

B. Jakobsen and K. Niss. “Sub-cryostat Prototype-test” report, RUC/ESS HUGINN project, Work Unit 1b. Technical report, February 2017.

B. Jakobsen and K. Niss. “SANS multi-temperature cuvette holder” Design report, RUC/ESS HUGINN project, Work Unit 3a. Technical report, October 2016.

B. Jakobsen and K. Niss. “Proof of Concept” report, RUC/ESS HUGINN project, Work Unit 1a. Technical report, July 2016.

B. Jakobsen. In-situ studies of bulk deformation structures: Static properties under load and Dynamics during deformation. Ph.d. thesis, Roskilde University, 2006. arXiv:0708.3986v1 [cond-mat.mtrl-sci]. [ http ]

K. Niss and B. Jakobsen. Dielectric and Shear Mechanical Relaxation in Glass Forming Liquids –- A thorough analysis and experimental test of the DiMarzio-Bishop model. Master thesis, Roskilde University, 2003. Text nr. 424 in "Tekster fra IMFUFA". [ .html ]

K. Niss and B. Jakobsen. Hopf bifurcation and topology in fluid flow (in danish). Project thesis, Roskilde University, 2002. Text nr. 412 in "Tekster fra IMFUFA". [ .ps ]

Proceedings

W. Pantleon, C. Wejdemann, B. Jakobsen, U. Lienert, and H. Poulsen. Advances in characterization of deformation structures by high resolution reciprocal space mapping. In N. Hansen, D. J. Jensen, S. Nielsen, H. Poulsen, and B. Ralph, editors, Proceedings of the 31st Risø International Symposium on Materials Science: Challenges in materials science and possibilities in 3D and 4D characterization techniques, pages 79–100. Risø National Laboratory for Sustainable Energy, Technical University of Denmark, 2010.

B. Jakobsen, U. Lienert, J. Almer, W. Pantleon, and H. Poulsen. Properties and dynamics of bulk subgrains probed in-situ using a novel x-ray diffraction method. Materials Science Forum, 550:613–618, 2007. Proceedings of ”Fundamentals of Deformation and Annealing Symposium´´, Manchester, 2006. [ http ]

U. Lienert, J. Almer, B. Jakobsen, W. Pantleon, H. Poulsen, D. Hennessy, C. Xiao, and R. Suter. 3-dimensional characterization of polycrystalline bulk materials using high-energy synchrotron radiation. Materials Science Forum, 539–543:2353--2358, 2007. Proceedings of ”International Conference on Processing & Manufacturing Of Advanced Materials (THERMEC) 2006´´.

W. Pantleon, B. Jakobsen, U. Lienert, J. Almer, C. Gundlach, and H. F. Poulsen. In-situ observation of individual subgrains by 3dxrd during deformation and recovery. In A. S. Khan and R. Kazmiy, editors, Anisotropy, Texture, Dislocations and Multiscale Modeling in Finite Plasticity & Viscoplasticity, and Metal Forming –- Proceedings of PLASTICITY '06: The Twelfth International Symposium on Plasticity and its Current Applications, pages 664–666. NEAT PRESS, 2006.

U. Lienert, J. Almer, B. Jakobsen, H. Poulsen, and W. Pantleon. Observation of dislocation structure evolution by analysis of x-ray peak profiles from individual bulk grains. In Proceedings of the 25th Risø International Symposium on Materials Science: Evolution of Deformation Microstructures in 3D, pages 417–422, 2004.

Other papers

Seeing the strains in deformed metals. In APS Science 2008 –- the annual report of the Advanced Photon Source at Argonne National Laboratory, ANL-08/24, pages 31–32. 2009. [ http ]

B. Jakobsen, U. Lienert, J. Almer, H. Sørensen, W. Pantleon, and H. Poulsen. Intermittent dynamics of dislocation structures during plastic deformation. In DANSYNC Annual Report. DANSYNC, 2005.

B. Jakobsen, U. Lienert, J. Almer, C. Gundlach, H. Poulsen, and W. Pantleon. Direct observation of individual subgrains in dislocation structures using ultra-high angular resolution x-ray diffraction. Unpublished draft for APS activity report 2004, used for GUP 4033 application, 2005.

B. Jakobsen, U. Lienert, J. Almer, H. Poulsen, and W. Pantleon. Direct observatio of the dynamics of individual dislocatio structures during plastic deformation. In DANSYNC Annual Report. DANSYNC, 2004.

B. Jakobsen, U. Lienert, J. Almer, H. Poulsen, and W. Pantleon. High reciprocal space resolution 3-dimensional x-ray diffraction. In Advanced Photon Source Activity Report 2003, number ANL-04/16. Argonne National Laboratory, December 2004. [ .PDF ]

International Presentations

B. Jakobsen, A. T. Holmes, H. Schneider, A. Pettersson, A. Hiess, and K. Niss. Huginn: Peltier-based temperature controlled sample platforms for neutron scattering. Poster, 2017. Dynamics of glass-forming liquids: will theory and experiment ever meet? (April 5 - 7, Carlsberg Academy, Copenhagen, Denmark).

B. Jakobsen and K. Niss. Peltier based temperature controlled sample platforms for neutron scattering. Oral presentation, 2015. IKON9 - The Ninth In-Kind Contributions Meeting for Neutron Science for ESS (September 21–22, Lund, Sweeden).

T. Hecksher, C. Gainaru, and B. Jakobsen. Broadband shear-mechanical spectroscopy on monohydroxy alcohols reveals mechanical short-chain polymer behavior corresponding to the dielectric debye process. Poster, 2015. International workshop on Viscous Liquids and the Glass Transition (XIII) (May 28–30, Søminestationen, Denmark).

T. Hecksher, C. Gainaru, and B. Jakobsen. Broadband shear-mechanical spectroscopy on monohydroxy alcohols reveals mechanical short-chain polymer behavior corresponding to the dielectric debye process. Poster, 2014. Liquids 2014, the 9th Liquid Matter Conference (July 21 – 25, Lisbon, Portugal).

B. Jakobsen and T. Hecksher. The debye-process in monohydroxy alcohols, as seen by broadband shear-mechanical spectroscopy: Is size important? Oral presentation, 2014. International workshop on Viscous Liquids and the Glass Transition (XII) (June 12–14, Søminestationen, Denmark).

B. Jakobsen, C. Maggi, K. Niss, T. Christensen, T. Hecksher, C. Gainaru, and J. Dyre. Shear-mechanical spectroscopy: Contrast between monohydroxy alcohols and van der Waals liquids. Invited Oral presentation, and abstract in collection, 2013. 7th International Discussion Meeting on Relaxations in Complex Systems (IDMRCS7) (July 21 – July 26, Barcelona, Spain).

B. Jakobsen. Experimental methods for measuring on viscoelastic glass-forming liquids. Oral presentation, and abstract in collectio, 2012. Nordic Conference on Ceramic and Glass Technology (December 6 – December 7, Risø, Denmark).

B. Jakobsen and T. Christensen. Effusivity based AC-calorimetry. Poster, 2012. 11th Lähnwitzseminar on Calorimetry (June 10 – June 14, Rostock-Warnemünde, Germany).

B. Jakobsen, T. Hecksher, K. Niss, T. Christensen, N. B. Olsen, and J. Dyre. Temperature-independent decoupling between the characteristic time scales of five independent linear response functions. Poster, 2011. International Workshop on Dynamics in Viscous Liquids III (March 30 – April 2, Rome, Italy).

B. Jakobsen, T. Hecksher, K. Niss, D. Gundermann, T. Christensen, N. B. Olsen, and J. Dyre. Coming the timescale from ac-calorimetric measurements to the timescales from four other response functions. Poster, 2010. 11th Lähnwitzseminar on Calorimetry (June 6–11, Rostock, Germany).

B. Jakobsen, T. Hecksher, K. Niss, D. Gundermann, T. Christensen, N. B. Olsen, and J. Dyre. Comison of the characteristic timescale from 5 independent response functions. Oral presentation, and abstract in collection, 2010. XII International Workshop on Complex Systems (March 15-18, Andalo, Trento, Italy). The temperature dependency of the characteristic timescale of the structural relaxation is a major ameter when characterizing viscous liquids. However, it is not possible to assign one unique timescale, as this depends on the type of response which is analyzed. Likewise the temperature dependency might also depend on the probed response function.

In this work we come time scales from 5 different, independent, response functions which can all be measured under identical conditions in our laboratory: Shear modulus [1,2], adiabatic bulk modulus [3,2], longitudinal thermal expansion coefficient [4,5], longitudinal specific heat [6] and dielectric response. The data presented is on the molecular glass-former tetramethyl-tetraphenyl-trisiloxane (the Dow Corning DC704 diffusion-pump oil).

Based on this data the differences in absolute timescale and temperature dependency between the response functions are discussed. We conclude that the shear modulus is faster than all the other response functions, and that the timescales generally follow each other very closely.

[1] Christensen and Olsen, Rev. Sci. Instr. (1995) 66, 5019.
[2] Hecksher et al. In progress.
[3] Christensen and Olsen, Phys. Rev. B (1994) 49, 15396.
[4] Bauer et al. Non-Cryst. Solids (2000) 262, 276.
[5] Niss et al. In progress.
[6] Christensen and Dyre, Phys. Rev. E (2008) 78, 021501; Jakobsen, Olsen, and Christensen, arXiv:0809.4617 [cond-mat.soft] (2008).

B. Jakobsen, K. Niss, C. Maggi, N. B. Olsen, T. Christensen, and J. C. Dyre. Secondary relaxation observed by broadband shear-mechanical spectroscopy. Invited Oral presentation, and abstract in collection, 2009. 6th International Discussion Meeting on Relaxations in Complex Systems (IDMRCS6) (August 30 – September 5, Rome, Italy). The major source for information on secondary relaxations is dielectric spectroscopy. The connection between dielectric response and the more fundamental mechanical relaxation is, however, not trivial. The piezoelectric shear-modulus gauge [1] allows for direct studies of the frequency dependent shear modulus in a frequency range from 1mHz to 10KHz, on liquids with moduli in the MPa to GPa range. Hence the method is well suited for studying the shear-mechanical signature of secondary relaxations. In this presentation we review our existing shear-mechanical data [2] with focus on how the phenomenology of the secondary relaxation is seen in the shear modulus. It is generally observed that when a secondary process is seen by dielectric relaxation it is also seen in the shear modulus, but phenomenological differences exist. The loss peak of the process is shifted to higher frequencies and the strength relative to the alpha relaxation is larger in the shear modulus comed to the dielectric. The phenomenological differences are furthermore discussed in terms of the Gemant-DiMarzio-Bishop model [3].
[1] T. Christensen and N. B. Olsen, Rev. Sci. Instrum. 66 (1995) 5019 .
[2] B. Jakobsen, K. Niss, and N. B. Olsen, J. Chem. Phys. 123 (2005) 234511. C. Maggi et al., J. Phys. Chem. B 112 (2008) 16320. B. Jakobsen et al., J. Chem. Phys. 129 (2008) 184502.
[3] K. Niss, B. Jakobsen, and N. B. Olsen, J. Chem. Phys. 123 (2005) 234510.

B. Jakobsen, N. B. Olsen, and T. Christensen. Frequency-dependent specific heat from thermal effusion in spherical geometry. Oral presentation, and abstract in collection, 2008. Fragility of Viscous Liquids: Cause(s) and Consequences (October 8-10, Copenhagen, Denmark).

B. Jakobsen, C. Maggi, T. Christensen, and J. C. Dyre. Broadband shear mechanical and dielectric investigation of monohydroxy alcohols close to the glass transition temperature. Poster presentation, and abstract in collection, 2008. Fragility of Viscous Liquids: Cause(s) and Consequences (October 8-10, Copenhagen, Denmark).

B. Jakobsen, C. Maggi, T. Christensen, and J. C. Dyre. Broadband shear mechanical and dielectric investigation of monohydroxy alcohols close to the glass transition temperature. Poster presentation, 2008. XI International Workshop on Complex Systems (March 17-20, Andalo, Trento, Italy).

B. Jakobsen, U. Lienert, J. Almer, W. Pantleon, and H. F. Poulsen. Properties and dynamics of bulk subgrains, probed in-situ using a novel X-ray diffraction method. Oral presentation, and abstract in collection, 2006. Fundamentals of Deformation and Annealing Symposium (September 5-7, Manchester, UK).

B. Jakobsen, U. Lienert, J. Almer, H. F. Poulsen, and W. Pantleon. Ultra-high angular resolution 3DXRD for observing bulk subgrains and their dynamic. Oral presentation, and abstract in collection, 2006. 14'th International Conference on the Strength of Materials ICSMA14 (June 4-9, Xi'an, China).

K. Niss and B. Jakobsen. Dielectric and shear mechanical relaxation in viscous liquids: Are they connected? Oral presentation, 2003. International workshop on Viscous Liquids and the Glass Transition (III) (May 9-11, Søminestationen, Denmark).

National Presentations

B. Jakobsen. Advanced sample enviroments for neutron and X-ray scattering. Oral presentation, 2018. 10th Annual DanScatt Meeting and 47th Danish Crystallographers Meeting 2018 (31 May - 1 June 2018, Roskilde University, Roskilde, Denmark).

B. Jakobsen. Fast and stable heating and cooling of samples. Invited Oral presentation, 2018. Neutron and Synchrotron Sample Environment Workshop (SEW2018) (2 - 3 May 2018, Sandbjerg Estate,Sønderborg Denmark).

B. Jakobsen. Fast and stable heating and cooling of samples. Invited Oral presentation, 2018. Danish Instruments for Big Science (DIBS18) (January 22, Aarhus University, Aarhus, Denmark).

B. Jakobsen, A. T. Holmes, H. Schneider, A. Pettersson, A. Hiess, and K. Niss. Huginn: Peltier-based temperature controlled sample platforms for neutron scattering. Poster, 2017. Danscatt Annual meeting (June 1 - 2, SDU, Odense, Denmark).

B. Jakobsen, T. Hecksher, K. Niss, D. Gundermann, T. Christensen, N. B. Olsen, and J. Dyre. Investigation of the uniqueness of the temperature dependence of the characteristic timescale in glass-forming liquids. Oral presentation, and abstract in collection, 2010. Annual meeting of Danish Physical Society (June 22-23, Nyborg, Denmark).

B. Jakobsen, C. Maggi, T. Christensen, and J. C. Dyre. Broadband shear mechanical and dielectric investigation of monohydroxy alcohols close to the glass transition temperature. Poster presentation, 2008. Annual meeting of the Danish Physical Society (June 17-18, Nyborg, Denmark).

B. Jakobsen, H. F. Poulsen, U. Lienert, J. Almer, S. D. Shastri, H. O. Sørensen, C. Gundlach, and W. Pantleon. Formation and subdivision of deformation structures. Oral presentation, and abstract in collection, 2006. 36th Danish Crystallographic Meeting, 8th DANSYNC Meeting & 4th DANSSK Meeting (May 16-17, Odense, Denmark).

B. Jakobsen, U. Lienert, J. Almer, H. Poulsen, and W. Pantleon. Ultra-high angular resolution 3dxrd for observing bulk subgrains. Poster presentation, and abstract in collection (P13), 2005. 35th Danish Crystallographic Meeting & 7th DANSYNC Meeting (May 25-26, Sandbjerg Estate, Denmark).

K. Niss, B. Jakobsen, and N. B. Olsen. Connection between shear mechanical relaxation and dielectric relaxation in viscoelastic liquids. Poster presentation, 2003. Annual meeting of the Danish Physical Society (June 12-13, Nyborg, Denmark).

B. Jakobsen, K. Niss, and M. Brøns. Streamline topologies of the periodic flow behind a cylinder. Poster presentation, 2002. Annual meeting of the Danish Physical Society (May 30-31, Nyborg, Denmark).

Publications and Presentations