1,202 research outputs found
Integration Schemes for Dissipative Particle Dynamics Simulations: From Softly Interacting Systems Towards Hybrid Models
We examine the performance of various commonly used integration schemes in
dissipative particle dynamics simulations. We consider this issue using three
different model systems, which characterize a variety of different conditions
often studied in simulations. Specifically we clarify the performance of
integration schemes in hybrid models, which combine microscopic and meso-scale
descriptions of different particles using both soft and hard interactions. We
find that in all three model systems many commonly used integrators may give
rise to surprisingly pronounced artifacts in physical observables such as the
radial distribution function, the compressibility, and the tracer diffusion
coefficient. The artifacts are found to be strongest in systems, where
interparticle interactions are soft and predominated by random and dissipative
forces, while in systems governed by conservative interactions the artifacts
are weaker. Our results suggest that the quality of any integration scheme
employed is crucial in all cases where the role of random and dissipative
forces is important, including hybrid models where the solvent is described in
terms of soft potentials
Recommended from our members
Decreased monsoon precipitation in the Northern Hemisphere due to anthropogenic aerosols
The Northern Hemisphere monsoons are an integral component of Earth's hydrological cycle and affect the lives of billions of people. Observed precipitation in the monsoon regions underwent substantial changes during the second half of the 20th century, with drying from the 1950s to mid-1980s and increasing precipitation in recent decades. Modeling studies suggest anthropogenic aerosols has been a key factor driving changes in tropical and monsoon precipitation. Here we apply detection and attribution methods to determine whether observed changes are driven
by human influences using fingerprints of individual forcings (i.e. greenhouse gas, anthropogenic aerosol and natural) derived from climate models. The results show that the observed changes can only be explained when including the influence of anthropogenic aerosols, even after accounting for internal climate variability. Anthropogenic aerosol, not greenhouse gas or natural forcing, has been the dominant influence on Northern Hemisphere monsoon precipitation over the second half of the 20th century
The TIGRE gamma-ray telescope
TIGRE is an advanced telescope for gamma-ray astronomy with a few arcmin resolution. From 0.3 to 10 MeV it is a Compton telescope. Above 1 MeV, its multi-layers of double sided silicon strip detectors allow for Compton recoil electron tracking and the unique determination for incident photon direction. From 10 to 100 MeV the tracking feature is utilized for gamma-ray pair event reconstruction. Here we present TIGRE energy resolutions, background simulations and the development of the electronics readout system
Who needs a stapling device for haemorrhoidectomy, if one has the radiofrequency device?
Peer reviewedPublisher PD
Mode Repulsion and Mode Coupling in Random Lasers
We studied experimentally and theoretically the interaction of lasing modes
in random media. In a homogeneously broadened gain medium, cross gain
saturation leads to spatial repulsion of lasing modes. In an inhomogeneously
broadened gain medium, mode repulsion occurs in the spectral domain. Some
lasing modes are coupled through photon hopping or electron absorption and
reemission. Under pulsed pumping, weak coupling of two modes leads to
synchronization of their lasing action. Strong coupling of two lasing modes
results in anti-phased oscillations of their intensities.Comment: 13 pages, 4 figure
Fluctuations of radiation from a chaotic laser below threshold
Radiation from a chaotic cavity filled with gain medium is considered. A set
of coupled equations describing the photon density and the population of gain
medium is proposed and solved. The spectral distribution and fluctuations of
the radiation are found. The full noise is a result of a competition between
positive correlations of photons with equal frequencies (due to stimulated
emission and chaotic scattering) which increase fluctuations, and a suppression
due to interaction with a gain medium which leads to negative correlations
between photons. The latter effect is responsible for a pronounced suppression
of the photonic noise as compared to the linear theory predictions.Comment: 7 pages, 5 figures; expanded version, to appear in Phys. Rev.
Factors influencing the catalytic oxidation of benzyl alcohol using supported phosphine-capped gold nanoparticles
Open Access Article. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.Two phosphine-stabilised gold clusters, Au101(PPh3)21Cl5 and Au9(PPh3)8(NO3)3, were deposited and activated on anatase TiO2 and fumed SiO2. These catalysts showed an almost complete oxidation of benzyl alcohol (>90%) within 3 hours at 80 °C and 3 bar O2 in methanol with a high substrate-to-metal molar ratio of 5800 and turn-over frequency of 0.65 sâ1. Factors influencing catalytic activity were investigated, including metalâsupport interaction, effects of heat treatments, chemical composition of gold clusters, the size of gold nanoparticles and catalytic conditions. It was found that the anions present in gold clusters play a role in determining the catalytic activity in this reaction, with NO3â diminishing the catalytic activity. High catalytic activity was attributed to the formation of large gold nanoparticles (>2 nm) that coincides with partial removal of ligands which occurs during heat treatment and catalysis. Selectivity towards the formation of methyl benzoate can be tuned by selection of the reaction temperature. The catalysts were characterised using transmission electron microscopy, UV-vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy
Towards Better Integrators for Dissipative Particle Dynamics Simulations
Coarse-grained models that preserve hydrodynamics provide a natural approach
to study collective properties of soft-matter systems. Here, we demonstrate
that commonly used integration schemes in dissipative particle dynamics give
rise to pronounced artifacts in physical quantities such as the compressibility
and the diffusion coefficient. We assess the quality of these integration
schemes, including variants based on a recently suggested self-consistent
approach, and examine their relative performance. Implications of
integrator-induced effects are discussed.Comment: 4 pages, 3 figures, 2 tables, accepted for publication in Phys. Rev.
E (Rapid Communication), tentative publication issue: 01 Dec 200
Freezing by Monte Carlo Phase-Switch
We describe a Monte Carlo procedure which allows sampling of the disjoint
configuration spaces associated with crystalline and fluid phases, within a
single simulation. The method utilises biased sampling techniques to enhance
the probabilities of gateway states (in each phase) which are such that a
global switch (to the other phase) can be implemented. Equilibrium
freezing-point parameters can be determined directly; statistical uncertainties
prescribed transparently; and finite-size effects quantified systematically.
The method is potentially quite general; we apply it to the freezing of hard
spheres.Comment: 5 pages, 2 figure
- âŠ