| 1. |
- Argun, Aykut, et al.
(författare)
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Enhanced force-field calibration via machine learning
- 2020
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Ingår i: Applied Physics Reviews. - : AIP Publishing. - 1931-9401. ; 7:4
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Tidskriftsartikel (refereegranskat)abstract
- The influence of microscopic force fields on the motion of Brownian particles plays a fundamental role in a broad range of fields, including soft matter, biophysics, and active matter. Often, the experimental calibration of these force fields relies on the analysis of the trajectories of the Brownian particles. However, such an analysis is not always straightforward, especially if the underlying force fields are non-conservative or time-varying, driving the system out of thermodynamic equilibrium. Here, we introduce a toolbox to calibrate microscopic force fields by analyzing the trajectories of a Brownian particle using machine learning, namely, recurrent neural networks. We demonstrate that this machine-learning approach outperforms standard methods when characterizing the force fields generated by harmonic potentials if the available data are limited. More importantly, it provides a tool to calibrate force fields in situations for which there are no standard methods, such as non-conservative and time-varying force fields. In order to make this method readily available for other users, we provide a Python software package named DeepCalib, which can be easily personalized and optimized for specific force fields and applications. This package is ideal to calibrate complex and non-standard force fields from short trajectories, for which advanced specific methods would need to be developed on a case-by-case basis.
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| 2. |
- Cichos, F., et al.
(författare)
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Machine learning for active matter
- 2020
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Ingår i: Nature Machine Intelligence. - : Springer Science and Business Media LLC. - 2522-5839. ; 2:2, s. 94-103
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Tidskriftsartikel (refereegranskat)abstract
- The availability of large datasets has boosted the application of machine learning in many fields and is now starting to shape active-matter research as well. Machine learning techniques have already been successfully applied to active-matter data-for example, deep neural networks to analyse images and track objects, and recurrent nets and random forests to analyse time series. Yet machine learning can also help to disentangle the complexity of biological active matter, helping, for example, to establish a relation between genetic code and emergent bacterial behaviour, to find navigation strategies in complex environments, and to map physical cues to animal behaviours. In this Review, we highlight the current state of the art in the application of machine learning to active matter and discuss opportunities and challenges that are emerging. We also emphasize how active matter and machine learning can work together for mutual benefit. This Review surveys machine learning techniques that are currently developed for a range of research topics in biological and artificial active matter and also discusses challenges and exciting opportunities. This research direction promises to help disentangle the complexity of active matter and gain fundamental insights for instance in collective behaviour of systems at many length scales from colonies of bacteria to animal flocks.
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| 3. |
- Mirzov, Oleg, et al.
(författare)
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Direct exciton quenching in single molecules of MEH-PPV at 77 K
- 2004
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 386:4-6, s. 286-290
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescence blinking behaviour was observed for single molecules of the conjugated polymer poly[2-methoxy,5-(2'-ethylhexyloxy)-p-phenylene-vinylene] (MEH-PPV) at 77 and 300 K. No strict qualitative dependence on temperature was observed, despite of the expected suppression of exciton migration at the low temperature. We assume MEH-PPV molecules to form dense nanoparticles with a characteristic size of about 10 nm at the largest. In such small nanoparticles exciton can be efficiently quenched by a photogenerated quencher due to Forster transfer just after a few hops over the polymer nanoparticle. Thus, long-distance exciton migration is not necessary to have strong fluorescence intensity fluctuations. (C) 2004 Elsevier B.V. All rights reserved.
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| 4. |
- Mirzov, Oleg, et al.
(författare)
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Fluorescence blinking in MEH-PPV single molecules at low temperature
- 2005
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 112:1-4, s. 353-356
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescence intensity transients of single molecules of the conjugated polymer poly[2-methoxy,5-(2-ethylhexyloxy)-p-phenylene-vinylene] (MEH-PPV) were studied at 15 K. Fluorescence blinking behavior was observed despite the expected low-temperature suppression of energy migration in such disordered molecular systems. Presence of the fluorescence blinking effect at 15K indicates that the single molecules possess a collapsed conformation with characteristic size of not more than several nanometers, which corresponds to only a few exciton hops over a polymer chain. (c) 2004 Elsevier B.V. All rights reserved.
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| 5. |
- Mirzov, Oleg, et al.
(författare)
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Large spectral diffusion of conjugated polymer single molecule fluorescence at low temperature
- 2005
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614. ; 408:4-6, s. 317-321
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Tidskriftsartikel (refereegranskat)abstract
- The conductive polymer poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4- phenylene vinylene) (MEH-PPV) was investigated by means of single molecule spectroscopy at 15 K. MEH-PPV single chains were deposited onto a surface from a toluene solution and covered with a polymer cap layer spin-coated from an aqueous solution for protection from air. The MEH-PPV molecules exhibited large fluorescence spectral diffusion with the range reaching 1000 cm(-1). We concluded that conformational changes, affecting dispersive interactions and conjugation length, is the most probable mechanism of the observed effect. It is the matrix-free environment that allows the MEH-PPV chains to undergo sufficiently large conformational changes even at low temperature. (c) 2005 Elsevier B.V. All rights reserved.
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| 6. |
- Schmidt, Falko, 1992, et al.
(författare)
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Microscopic Engine Powered by Critical Demixing
- 2018
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Ingår i: Physical Review Letters. - 0031-9007. ; 120:6
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Tidskriftsartikel (refereegranskat)abstract
- We experimentally demonstrate a microscopic engine powered by the local reversible demixing of a critical mixture. We show that, when an absorbing microsphere is optically trapped by a focused laser beam in a subcritical mixture, it is set into rotation around the optical axis of the beam because of the emergence of diffusiophoretic propulsion. This behavior can be controlled by adjusting the optical power, the temperature, and the criticality of the mixture.
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| 7. |
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| 8. |
- Zenkevich, E.I., et al.
(författare)
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Ligand exchange dynamics and temperature effects upon formation of nanocomposites based on semiconductor CdSe/ZnS quantum dots and porphyrins: Ensemble and single object measurements
- 2012
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Ingår i: Macroheterocycles. - : Ivanovo State University of Chemistry and Technology. - 1998-9539. ; 5:2, s. 98-114
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Tidskriftsartikel (refereegranskat)abstract
- Dye molecules with pyridyl side substituents (porphyrins and heterocyclic perylene diimides) coordinatively attached to semiconductor CdSe/ZnS quantum dots (QDs) surface form quasi-stable QD-Dye nanocomposites of various geometry in the competition with capping molecules (tri-n-octyl phosphine oxide or long chain amines) exchange. This results in photoluminescence (PL) quenching of the QDs both due to Foerster resonance energy transfer and formation of non-radiative surface states. QD surface is inhomogeneous with respect to the involved attachment and detachment processes. The formation of QD-Porphyrin nanocomposites is realized at least two time scales (60 and 600 s), which is attributed to a reorganisation of tri-n-octylphosphine oxide capping shell. In a low temperature range of 220÷240 K related changes in QD absorption and emission reveal a phase transition of the capping shell (tri-n-octyl phosphine oxide and amine). In QD-Dye nanocomposites, this phase transition is enhanced considerably by only a few attached dye molecules and has impact on the QD core structure followed by changes of PL quenching and exciton-phonon coupling. A combination of ensemble and single molecule spectroscopy of QD-Dye nanocomposites reveals that few or even only one attached dye molecule change the surface distribution and energy of dye related surface trap states considerably. © ISUCT Publishing.
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