| 1. |
- Aristov, Maria, et al.
(författare)
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Separation of chiral colloidal particles in a helical flow field
- 2013
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 9:8, s. 2525-2530
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Tidskriftsartikel (refereegranskat)abstract
- Stereoisomeric molecules with opposite chirality, so-called enantiomers, often vary regarding their sensory, pharmacological and toxicological properties. Such enantiomer specific effects play a central role in the development, testing and evaluation of drugs, pesticides and food related products. Accordingly, efficient techniques for separation of chiral mixtures into enantiopure compounds are of enormous practical relevance. Most current enantiomer separation methods are based on enantioselective interactions with an auxiliary substance which has to be developed and optimized for different chiral molecules in an elaborate and costly process. Here, we experimentally demonstrate the separation of micron-sized chiral particles in a helical fluid flow which is created inside a microfluidic device patterned with slanted grooves. We observe that the retention time of particles in a helical flow field strongly depends on their chirality which leads to an effective chiral separation within the channel. Our experimental results are confirmed by numerical calculations which demonstrate how the coupling of rotational and translational degrees of freedom leads to differences in the trajectories of particles with opposite chirality. Since our separation mechanism does not rely on material specific interactions, this offers considerable advantages over existing methods. We expect that our approach can be also applied at nanometre length scales by using channels with smaller diameters and with an optimized geometry.
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| 2. |
- Behringer, H., et al.
(författare)
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Brownian dynamics simulations with hard-body interactions : Spherical particles
- 2012
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 137:16, s. 164108-
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Tidskriftsartikel (refereegranskat)abstract
- A novel approach to account for hard-body interactions in (overdamped) Brownian dynamics simulations is proposed for systems with non-vanishing force fields. The scheme exploits the analytically known transition probability for a Brownian particle on a one-dimensional half-line. The motion of a Brownian particle is decomposed into a component that is affected by hard-body interactions and into components that are unaffected. The hard-body interactions are incorporated by replacing the affected component of motion by the evolution on a half-line. It is discussed under which circumstances this approach is justified. In particular, the algorithm is developed and formulated for systems with space-fixed obstacles and for systems comprising spherical particles. The validity and justification of the algorithm is investigated numerically by looking at exemplary model systems of soft matter, namely at colloids in flow fields and at protein interactions. Furthermore, a thorough discussion of properties of other heuristic algorithms is carried out.
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| 3. |
- Behringer, Hans, et al.
(författare)
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Dynamics of biomolecular processes PREFACE
- 2013
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 87:5, s. 058501-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 4. |
- Bo, Stefano, et al.
(författare)
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Optimal stochastic transport in inhomogeneous thermal environments
- 2013
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 103:1, s. 10010-
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Tidskriftsartikel (refereegranskat)abstract
- We consider the optimization of the average entropy production in inhomogeneous temperature environments within the framework of stochastic thermodynamics. For systems modeled by Langevin equations (e.g. a colloidal particle in a heat bath) it has been recently shown that a space-dependent temperature breaks the time reversal symmetry of the fast velocity degrees of freedom resulting in an anomalous contribution to the entropy production of the overdamped dynamics. We show that optimization of entropy production is determined by an auxiliary deterministic problem formally analogous to motion on a curved manifold in a potential. The anomalous contribution to entropy plays the role of the potential and the inverse of the diffusion tensor is the metric. We also find that entropy production is not minimized by adiabatically slow, quasi-static protocols but there is a finite optimal duration for the transport process. As an example we discuss the case of a linearly space-dependent diffusion coefficient.
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| 5. |
- Bogunovic, L., et al.
(författare)
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Chiral particle separation by a nonchiral microlattice
- 2012
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 109:10, s. 100603-
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Tidskriftsartikel (refereegranskat)abstract
- We conceived a model experiment for a continuous separation strategy of chiral molecules (enantiomers) without the need of any chiral selector structure or derivatization agents: Microparticles that only differ by their chirality are shown to migrate along different directions when driven by a steady fluid flow through a square lattice of cylindrical posts. In accordance with our numerical predictions, the transport directions of the enantiomers depend very sensitively on the orientation of the lattice relative to the fluid flow.
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| 6. |
- Bogunovic, L., et al.
(författare)
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Valveless fluid actuation : Liebau’s principle fully integrated on the microfluidic scale
- 2013
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Ingår i: 17th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2013. ; , s. 182-184
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Konferensbidrag (refereegranskat)abstract
- In this contribution, we present the integration of valveless impedance pumping on the microfluidic scale. When a fluidic channel is periodically compressed at a point located asymmetrically with respect to an impedance mismatch in the system, an effective fluid flow is the result although no further moving parts such as valves are involved. Such an impedance mismatch could be e.g. a sudden reduction of the channel cross section. Four different types of impedance mismatches are being investigated concerning their response to different applied pressures and compression frequencies .A maximum fluid velocity of 25 }im/s and even a frequency dependent overall inversion of the flow direction could be observed.
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| 7. |
- Celani, A., et al.
(författare)
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Anomalous thermodynamics at the microscale
- 2012
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 109:26, s. 260603-
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Tidskriftsartikel (refereegranskat)abstract
- Particle motion at the microscale is an incessant tug-of-war between thermal fluctuations and applied forces on one side and the strong resistance exerted by fluid viscosity on the other. Friction is so strong that completely neglecting inertia - the overdamped approximation - gives an excellent effective description of the actual particle mechanics. In sharp contrast to this result, here we show that the overdamped approximation dramatically fails when thermodynamic quantities such as the entropy production in the environment are considered, in the presence of temperature gradients. In the limit of vanishingly small, yet finite, inertia, we find that the entropy production is dominated by a contribution that is anomalous, i.e., has no counterpart in the overdamped approximation. This phenomenon, which we call an entropic anomaly, is due to a symmetry breaking that occurs when moving to the small, finite inertia limit. Anomalous entropy production is traced back to futile phase-space cyclic trajectories displaying a fast downgradient sweep followed by a slow upgradient return to the original position.
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| 8. |
- Eichhorn, Ralf, et al.
(författare)
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Stochastic thermodynamics
- 2014
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Ingår i: Physica Scripta. - : IOP Publishing. - 0031-8949 .- 1402-4896. ; 89:4, s. 048001-
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Tidskriftsartikel (refereegranskat)
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| 9. |
- Kümmel, Felix, et al.
(författare)
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Circular Motion of Asymmetric Self-Propelling Particles
- 2013
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 110:19, s. 198302-
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Tidskriftsartikel (refereegranskat)abstract
- Micron-sized self-propelled (active) particles can be considered as model systems for characterizing more complex biological organisms like swimming bacteria or motile cells. We produce asymmetric microswimmers by soft lithography and study their circular motion on a substrate and near channel boundaries. Our experimental observations are in full agreement with a theory of Brownian dynamics for asymmetric self-propelled particles, which couples their translational and orientational motion.
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| 10. |
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