Biology:Fluctuation spectrum
In various areas of science, processes occur which have as a key feature the fluctuation of some quantity around its mean or equilibrium value. A fluctuation spectrum is the frequency spectrum of this. It essentially breaks the fluctuation down into individual frequencies contributing at different strengths.[lower-alpha 1] Peaks in the spectrum typically indicate frequencies—or equivalently, timescales—at which something of interest is happening.
A quantity may also be considered as fluctuating with respect to position rather than time. In this case the spectrum breaks the fluctuations down by spatial frequency, measured in cycles per unit distance rather than per unit time. A peak will indicate the length scale at which some structure or phenomenon repeats.
Examples
Phenomena which have been analysed using fluctuation spectra include
- hydrodynamic turbulence
- the collective behaviour of bacteria
- the maritime Casimir effect whereby surface waves on the sea create a force between two adjacent ships. This is usually attractive, but a 2017 analysis in terms of the spatial fluctuation spectrum of the waves predicts circumstances where the ships could instead be pushed apart.[1]
- the cosmic microwave background
- fluctuations in human heart rate
- population dynamics of a simulated ecosystem.[2]
Notes
- ↑ This is similar to the ear analysing air pressure variations into the audio frequencies which we hear.
References
- ↑ Lee, Alpha A; Vella, Dominic; Wettlaufer, John S (August 29, 2017). "Fluctuation spectra and force generation in nonequilibrium systems". Proceedings of the National Academy of Sciences 114 (35): 9255–9260. doi:10.1073/pnas.1701739114. PMID 28811368. Bibcode: 2017PNAS..114.9255L.
- ↑ Krumbeck, Yvonne; Yang, Qian; Constable, George W A; Rogers, Tim (15 June 2021). "Fluctuation spectra of large random dynamical systems reveal hidden structure in ecological networks". Nature Communications 12 (3625 (2021)): 3625. doi:10.1038/s41467-021-23757-x. PMID 34131115. Bibcode: 2021NatCo..12.3625K.
General references
- Paxton, Walter F.; Kistler, Kevin C.; Olmeda, Christine C.; Sen, Ayusman; St. Angelo, Sarah K. et al. (2004). "Catalytic Nanomotors: Autonomous Movement of Striped Nanorods". Journal of the American Chemical Society (American Chemical Society (ACS)) 126 (41): 13424–13431. doi:10.1021/ja047697z. ISSN 0002-7863. PMID 15479099.
- Soto, Rodrigo; Golestanian, Ramin (2014-02-10). "Self-Assembly of Catalytically Active Colloidal Molecules: Tailoring Activity Through Surface Chemistry". Physical Review Letters (American Physical Society (APS)) 112 (6): 068301. doi:10.1103/physrevlett.112.068301. ISSN 0031-9007. PMID 24580712. Bibcode: 2014PhRvL.112f8301S.
- Brandt, Erik G.; Braun, Anthony R.; Sachs, Jonathan N.; Nagle, John F.; Edholm, Olle (2011-05-04). "Interpretation of Fluctuation Spectra in Lipid Bilayer Simulations". Biophysical Journal 100 (9): 2104–2111. doi:10.1016/j.bpj.2011.03.010. ISSN 0006-3495. PMID 21539777. Bibcode: 2011BpJ...100.2104B.
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