1,304 research outputs found
Non-equilibrium forces following quenches in active and thermal matter
Non-equilibrium systems are known to exhibit long-ranged correlations due to
conservation of quantities like density or momentum. This, in turn, leads to
long-ranged fluctuation-induced (Casimir) forces, predicted to arise in a
variety of non-equilibrium settings. Here, we study such forces, which arise
transiently between parallel plates or compact inclusions in a gas of
particles, following a change ("quench") in temperature or activity of the
medium. Analytical calculations, as well as numerical simulations of passive or
active Brownian particles, indicate two distinct forces: (i) The immediate
effect of the quench is adsorption or desorption of particles of the medium to
the immersed objects, which in turn initiates a front of relaxing (mean)
density. This leads to time-dependent {\it density-induced forces}. (ii) A
long-term effect of the quench is that density fluctuations are modified,
manifested as transient (long-ranged) (pair-)correlations that relax
diffusively to their (short-ranged) steady-state limit. As a result, transient
{\it fluctuation-induced forces} emerge. We discuss the properties of
fluctuation-induced and density-induced forces as regards universality,
relaxation as a function of time, and scaling with distance between objects.
Their distinct signatures allow us to distinguish the two types of forces in
simulation data. Finally, we propose several scenarios for their experimental
observation.Comment: - Added Journal reference and DOI - Modified title - Fixed minor
typos - Added plot of Eq. (32) [16 pages, 11 figures
Response of active Brownian particles to shear flow
We study the linear response of interacting active Brownian particles in an
external potential to simple shear flow. Using a path integral approach, we
derive the linear response of any state observable to initiating shear in terms
of correlation functions evaluated in the unperturbed system. For systems and
observables which are symmetric under exchange of the and coordinates,
the response formula can be drastically simplified to a form containing only
state variables in the corresponding correlation functions (compared to the
generic formula containing also time derivatives). In general, the shear
couples to the particles by translational as well as rotational advection, but
in the aforementioned case of symmetry only translational advection is
relevant in the linear regime. We apply the response formulas analytically in
solvable cases and numerically in a specific setup. In particular, we
investigate the effect of a shear flow on the morphology and the stress of
confined active particles in interaction, where we find that the activity as
well as additional alignment interactions generally increase the response.Comment: 13 pages, 4 figure
Development of an integrated solar-fossil powered steam generation system for industrial applications
Das Poster gibt eine kurze Einführung in das Projekt SolSteam, in dem die Integration solaren Prozessdampfes in einen konventionellen Dampferzeuger untersucht wird
Appendix
This appendix contains data for the six research reports of the first issue of the Kiel Journal of Consumer Studies (KJCS)
Overshoots in stress strain curves: Colloid experiments and schematic mode coupling theory
The stress versus strain curves in dense colloidal dispersions under start-up
shear flow are investigated combining experiments on model core-shell
microgels, computer simulations of hard disk mixtures, and mode coupling
theory. In dense fluid and glassy states, the transient stresses exhibit first
a linear increase with the accumulated strain, then a maximum ('stress
overshoot') for strain values around 5%, before finally approaching the
stationary value, which makes up the flow curve. These phenomena arise in
well-equilibrated systems and for homogeneous flows, indicating that they are
generic phenomena of the shear-driven transient structural relaxation.
Microscopic mode coupling theory (generalized to flowing states by integration
through the transients) derives them from the transient stress correlations,
which first exhibit a plateau (corresponding to the solid-like elastic shear
modulus) at intermediate times, and then negative stress correlations during
the final decay. We introduce and validate a schematic model within mode
coupling theory which captures all of these phenomena and handily can be used
to jointly analyse linear and large-amplitude moduli, flow curves, and
stress-strain curves. This is done by introducing a new strain- and
time-dependent vertex into the relation between the the generalized shear
modulus and the transient density correlator.Comment: 21 pages, 13 figure
Editorial
Editorial of the first issue of the newly established Kiel Journal of Consumer Studies
Improving selectivity in catalytic hydrodefluorination by limiting SNV reactivity
Catalytic hydrodefluorination of perfluoroallylbenzene with Cp2TiH in THF is
unselective and yields a variety of previously unknown compounds,
predominantly activated in the allylic position. Several different mechanisms
have been examined in detail using solvent corrected (THF) DFT(M06-2X)
calculations for the archetypal perfluorinated olefin perfluoropropene and
perfluoroallylbenzene: (a) single electron transfer, (b)
hydrometallation/fluoride elimination, (c) σ-bond metathesis (allylic or
vinylic), and (d) nucleophilic vinylic substitution (SNV, w/o Ti–F contacts in
the TS). SNV is shown to be a competitive mechanism to hydrometallation and
proceeds via ionic species from which F-elimination is facile and unselective
leading to low selectivity in polar solvents. Subsequent experiments show that
selectivity can be increased in a non-polar solvent
Detection of Counterfeit by the Usage of Product Inherent Features
AbstractOne aspect of the economical dimension of sustainable business development is the protection of high value products from counterfeiting. This holds especially true for consumer goods since the sustainable manufacturing process gains a more and more important role, e.g. in the creation of a brand image. In this paper we propose a method for detecting counterfeit by capture of inherent features indissolubly linked with the product induced by the production process itself. Since a counterfeiter gains margin by the use of inferior production processes and material the differences between genuine product and counterfeit can be captured in an automated fashion. The proposed method not only renders the application of artificial security tags obsolete which helps reducing the material usage but also gives enhanced protection against counterfeiting as the inherent characteristics cannot be removed from the article
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