Search results for "Structure formation"
showing 10 items of 43 documents
Structure finding in cosmological simulations: the state of affairs
2013
The ever increasing size and complexity of data coming from simulations of cosmic structure formation demands equally sophisticated tools for their analysis. During the past decade, the art of object finding in these simulations has hence developed into an important discipline itself. A multitude of codes based upon a huge variety of methods and techniques have been spawned yet the question remained as to whether or not they will provide the same (physical) information about the structures of interest. Here we summarize and extent previous work of the "halo finder comparison project": we investigate in detail the (possible) origin of any deviations across finders. To this extent we decipher…
Late decaying 2-component dark matter scenario as an explanation of the AMS-02 positron excess
2016
The long standing anomaly in the positron flux as measured by the PAMELA and AMS-02 experiments could potentially be explained by dark matter (DM) annihilations. This scenario typically requires a large "boost factor" to be consistent with a thermal relic dark matter candidate produced via freeze-out. However, such an explanation is disfavored by constraints from CMB observations on energy deposition during the epoch of recombination. We discuss a scenario called late-decaying two-component dark matter (LD2DM), where the entire DM consists of two semi-degenerate species. Within this framework, the heavier species is produced as a thermal relic in the early universe and decays to the lighter…
Structure and dynamics of amphiphilic Janus spheres and spherocylinders under shear.
2019
We study the structure formation and flow properties of colloidal dispersions comprised of Janus spheres, Janus spherocylinders, and their mixtures, using hybrid molecular dynamics simulations that take into account hydrodynamic interactions. We systematically vary the Janus balance and the shape anisotropy of the particles, and explore a range of colloid volume fractions in the liquid regime of the phase diagram. At rest, Janus spheres with small hydrophobic patches form spherical micelles for all investigated colloid concentrations. In contrast, Janus spheres with an entirely hydrophobic hemisphere aggregate to larger worm-like micelles and network-like structures. Janus spherocylinders e…
Structural and morphological rearrangements in quenched poly(ethylene) by simultaneous SAXS/WAXS
2000
Structure formation by crystallization from the melt in a wide range of cooling rates (0.08-1 000°C/s) in low-density polyethylene has been studied by simultaneous small- and wide-angle X-ray scattering at the synchroton radiation source of DESY. The occurrence of two periodicities, characterized by different angular position of Bragg's maxima, was observed, pointing to the existence of two types of lamellar stacks, associated with two different long period values L 1 and L 2 (L 1 > L 2 ). L 1 depends on the cooling rate, whereas L 2 is almost constant. A comparison with isotactic polypropylene is performed, where a similar phenomenon takes place. While in the case of i-PP a definite correl…
Microscopic studies of surface morphology of high temperature superconductor thick layers
2004
Abstract The surface morphology and structure of the YBa2Cu3O7−δ superconductor ayers prepared on passive ceramic and single crystal substrates is studied by electron microscopy. The layers reveal features of structure formation.
Soliton staircases and standing strain waves in confined colloidal crystals
2009
We show by computer simulation of a two-dimensional crystal confined by corrugated walls that confinement can be used to impose a controllable mesoscopic superstructure of predominantly mechanical elastic character. Due to an interplay of the particle density of the system and the width D of the confining channel, "soliton staircases" can be created along both parallel confining boundaries, that give rise to standing strain waves in the entire crystal. The periodicity of these waves is of the same order as D. This mechanism should be useful for structure formation in the self-assembly of various nanoscopic materials.
Mechanical properties and accommodation processes on metallic interfaces
1998
Bimetallic joints Al/Pb, Al/Sn, Pb/Sn, Pb/Pb, etc. with clean interfaces, obtained by a special cold welding method, are used as a model of phase boundaries for investigation of accommodation processes and strength properties of interfaces. To reduce the volume diffusion-induced relaxation processes, investigations were carried out at relatively low temperatures 0.1-0.5 T m . The role of surface diffusion and the effect of phase boundary energy on the healing of micropore ensembles on interfaces was investigated. The accommodation processes on the phase boundaries are considered as a result of mechanoactivation of both the interaction and structure formation of such non-equilibrium systems.…
Confinement-induced screening of hydrodynamic interactions and spinodal decomposition: Multiscale simulations of colloid-polymer mixtures
2012
Phase separation kinetics of a colloid-polymer mixture confined between two planar repulsive walls is studied by a multiscale simulation approach. Colloids and polymers are described by particles interacting with continuous potentials suitable for molecular-dynamics simulation, while hydrodynamic interactions mediated by solvent particles are accounted for by the multiparticle collision dynamics method. Varying the distance D between the walls and the character of the boundary conditions, the interplay of structure formation parallel and perpendicular to the walls is studied, and the effect of hydrodynamics on the growth of domain size ld(t) with time t is elucidated. Only for slip boundary…
How does the pattern of grafting points influence the structure of one-component and mixed polymer brushes?
2005
Using Monte Carlo simulations of a coarse-grained bead-spring model we study the lateral structure formation of one-component polymer brushes in a bad solvent and of a mixed polymer brush upon increasing the incompatibility of the two species. We compare the morphology of the brush with a regular distribution of grafting points and with a random arrangement. Density or composition fluctuations of the grafting points enhance the formation of irregular structures but randomness prevents the formation of long-range order. Even small fluctuations of the grafting points are sufficient to pin the lateral structures of the brush.
Adsorption and structure formation of semiflexible polymers on spherical surfaces
2018
Abstract Rigid spheres with a short-range attractive potential are taken as a coarse-grained model of vesicles, which contain a solution of semiflexible polymers in their interior. Assuming good solvent conditions with an implicit description of the solvent, effective monomers experience bond-length and bond-angle potentials as well as excluded-volume interaction. Due to the attractive vesicle surface, phase separation occurs between a thin shell of adsorbed monomers at the surface and a rather dilute, and therefore, disordered polymer solution in the sphere interior. While at a planar attractive surface the wormlike chains would exhibit liquid crystalline (nematic and smectic) order, the c…