Jesper S. Hansen

Jesper S. Hansen
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Jesper S. Hansen

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Pub Categories

Physics - Chemical Physics (6)
Physics - Soft Condensed Matter (4)
Physics - Computational Physics (4)
Physics - Materials Science (2)
Physics - Mesoscopic Systems and Quantum Hall Effect (2)
Physics - Statistical Mechanics (1)
Physics - Atomic and Molecular Clusters (1)
Physics - Other (1)

Publications Authored By Jesper S. Hansen

In this paper the response of ionic systems subjected to a spatially varying electric field is studied. Following the Nernst-Planck equation, two forces driving the mass flux are present, namely, the concentration gradient and the electric potential gradient. The mass flux due to the concentration gradient is modelled through Fick's law, and a new constitutive relation for the mass flux due to the potential gradient is proposed. Read More

One century ago pioneering dielectric results obtained for water and n-alcohols triggered the advent of molecular rotation diffusion theory considered by Debye to describe the primary dielectric absorption in these liquids. Comparing dielectric, viscoelastic, and light scattering results we unambiguously demonstrate that the structural relaxation appears only as a high-frequency shoulder in the dielectric spectra of water. In contrast, the main dielectric peak is related to a supramolecular structure, analogous to the Debye-like peak observed in mono-alcohols. Read More

Systems of Cooee bitumen and water up to 4 mass % are studied by molecular dynamics simula- tions. The cohesive energy density of the system is shown to decrease with an increasing water content. This decrease is due mainly to an increase in potential energy which is not high enough to counterbalance the increase in volume due to the addition of water. Read More

We discuss the plastic behavior of an amorphous matrix reinforced by hard particles. A mesoscopic depinning-like model accounting for Eshelby elastic interactions is implemented. Only the effect of a plastic disorder is considered. Read More

RUMD is a general purpose, high-performance molecular dynamics (MD) simulation package running on graphical processing units (GPU's). RUMD addresses the challenge of utilizing the many-core nature of modern GPU hardware when simulating small to medium system sizes (roughly from a few thousand up to hundred thousand particles). It has a performance that is comparable to other GPU-MD codes at large system sizes and substantially better at smaller sizes. Read More

The rheology and molecular structure of a model bitumen (Cooee bitumen) under shear are investigated in the non-Newtonian regime using non-equilibrium molecular dynamics simulations. The shear viscosity, normal stress differences and pressure of the bitumen mixture are computed at different shear rates and different temperatures. The model bitumen is shown to be a shear-thinning fluid at all temperatures. Read More

Asphaltene and smaller aromatic molecules tend to form linear nanoaggregates in bitumen.Over the years bitumen undergoes chemical aging and during this process, the size of the nanoaggregate increases. This increase is associated with an increase in viscosity and brittleness of the bitumen, eventually leading to road deterioration. Read More

We study chemical aging in "COOEE bitumen" using molecular dynamic simulations. This model bitumen is composed of four realistic molecule types: saturated hydrocarbon, resinous oil, resin, and asphaltene. The aging reaction is modelled by the chemical reaction: "2 resins $\rightarrow$ 1 asphaltene". Read More

We propose a four-component molecular model of bitumen. The model includes realistic chemical constituents and introduces a coarse-graining level that suppresses the highest frequency modes. Molecular dynamics simulations of the model are being carried out using Graphic-Processor-Units based software in time spans in order of microseconds, and this enables the study of slow relaxation processes characterizing bitumen. Read More

According to standard liquid-state theory repulsive and attractive pair forces play distinct roles for the physics of liquids. This paradigm is put into perspective here by demonstrating a continuous series of pair potentials that have virtually the same structure and dynamics, although only some of them have attractive forces of significance. Our findings reflect the fact that the motion of a given particle is determined by the total force on it, whereas the quantity usually discussed in liquid-state theory is the individual pair force. Read More

This paper compares the Wolf method to the shifted forces (SF) method for efficient computer simulation of isotropic systems interacting via Coulomb forces, taking results from the Ewald summation method as representing the true behavior. We find that for the Hansen-McDonald molten salt model the SF approximation overall reproduces the structural and dynamical properties as accurately as does the Wolf method. It is shown that the optimal Wolf damping parameter depends on the property in focus, and that neither the potential energy nor the radial distribution function are useful measures for the convergence of theWolf method to the Ewald summation method. Read More