More Like this

1. Pattern formation in Faraday instability—experimental validation of theoretical models

   https://doi.org/10.1098/rsta.2022.0081  

   Dinesh, B. ; Livesay, J. ; Ignatius, I. B. ; Narayanan, R. ( April 2023 , Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences)

   n/a (Ed.)

   Two types of resonance-derived interfacial instability are reviewed with a focus on recent work detailing the effect of side walls on interfacial mode discretization. The first type of resonance is the mechanical Faraday instability, and the second is electrostatic Faraday instability. Both types of resonance are discussed for the case of single-frequency forcing. In the case of mechanical Faraday instability, inviscid theory can forecast the modal forms that one might expect when viscosity is taken into account. Experiments show very favourable validation with theory for both modal forms and onset conditions. Lowering of gravity is predicted to shift smaller wavelengths or choppier modes to lower frequencies. This is also validated by experiments. Electrostatic resonant instability is shown to lead to a pillaring mode that occurs at low wavenumbers, which is akin to Rayleigh Taylor instability. As in the case of mechanical resonance, experiments show favourable validation with theoretical predictions of patterns. A stark difference between the two forms of resonance is the observation of a gradual rise in the negative detuning instability in the case of mechanical Faraday and a very sharp one in the case of electrostatic resonance.

   This article is part of the theme issue ‘New trends in pattern formation and nonlinear dynamics of extended systems’.

    

   more » « less
2. Mimicry of a biophysical pathway leads to diverse pollen-like surface patterns

   https://doi.org/10.1073/pnas.1919060117  

   Liu, Jiaqi ; Radja, Asja ; Gao, Yuchong ; Yin, Rui ; Sweeney, Alison ; Yang, Shu ( April 2020 , Proceedings of the National Academy of Sciences)

   A ubiquitous structural feature in biological systems is texture in extracellular matrix that gains functions when hardened, for example, cell walls, insect scales, and diatom tests. Here, we develop patterned liquid crystal elastomer (LCE) particles by recapitulating the biophysical patterning mechanism that forms pollen grain surfaces. In pollen grains, a phase separation of extracellular material into a pattern of condensed and fluid-like phases induces undulations in the underlying elastic cell membrane to form patterns on the cell surface. In this work, LCE particles with variable surface patterns were created through a phase separation of liquid crystal oligomers (LCOs) droplet coupled to homeotropic anchoring at the droplet interface, analogously to the pollen grain wall formation. Specifically, nematically ordered polydisperse LCOs and isotropic organic solvent (dichloromethane) phase-separate at the surface of oil-in-water droplets, while, different LCO chain lengths segregate to different surface curvatures simultaneously. This phase separation, which creates a distortion in the director field, is in competition with homeotropic anchoring induced by sodium dodecyl sulfate (SDS). By tuning the polymer chemistry of the system, we are able to influence this separation process and tune the types of surface patterns in these pollen-like microparticles. Our study reveals that the energetically favorable biological mechanism can be leveraged to offer simple yet versatile approaches to synthesize microparticles for mechanosensing, tissue engineering, drug delivery, energy storage, and displays.

    

   more » « less
3. Evaluating ENSO's Spatiotemporal Complexity in the CWB CFS 1‐Tiered Model Hindcasts

   https://doi.org/10.1029/2022JD038200  

   Kim, Ji‐Won ; Chang, Ting‐Huai ; Lee, Ching‐Teng ; Yu, Jin‐Yi ( July 2023 , Journal of Geophysical Research: Atmospheres)

   Using hindcasts produced by a coupled climate model, this study evaluates whether the model can forecast the observed spatiotemporal complexity in the El Niño−Southern Oscillation (ENSO) during the period 1982−2011: the eastern Pacific (EP), central Pacific‐I (CP‐I) and ‐II (CP‐II) types of El Niño, and the multi‐year evolution events of El Niño occurred in 1986–1988 (i.e., 1986/87/88 El Niño) and La Niña occurred in 1998–2000 (i.e., 1998/99/00 La Niña). With regard to the spatial complexity, it is found that the CP‐I type of El Niño is the easiest to hindcast, the CP‐II is second, and the EP is most difficult to hindcast as its amplitude is significantly underestimated in the model used here. The model deficiency in hindcasting the EP El Niño is related to a warm bias in climatological sea surface temperatures (SSTs) in the tropical eastern Pacific. This warm bias is related to model biases in the strengths of the Pacific Walker circulation and South Pacific high, both of which are notably weaker than observed. As for the temporal complexity, the model successfully hindcasts the multi‐year evolution of the 1998/99/00 La Niña but fails to accurately hindcast the 1986/87/88 El Niño. This contrasting model performance in hindcasting multi‐year events is found to be related to a cold bias in climatological SSTs in the tropical central Pacific. This cold bias result enables the model La Niña, but not El Niño, to activate intrabasin tropical‒subtropical interactions associated with the Pacific Meridional Mode that produce the multi‐year evolution pattern.

    

   more » « less
4. Orientational Ordering within Semiconducting Polymer Fibrils

   https://doi.org/10.1002/adfm.202102522  

   Mukherjee, Subhrangsu ; Gann, Eliot ; Nahid, Masrur Morshed ; McAfee, Terry ; Herzing, Andrew A. ; DeLongchamp, Dean M. ; Ade, Harald ( May 2021 , Advanced Functional Materials)

   Due to a general paucity of suitable characterization methods, the internal orientational ordering of polymer fibrils has rarely been measured despite its importance particularly for semi‐conducting polymers. An emerging tool with sensitivity to bond orientation is polarized resonant soft X‐ray scattering (P‐RSoXS). Here, P‐RSoXS reveals the molecular arrangement within fibrils (if type I or type II fibrils), the extent of orientation in the fibril crystal, and an explicit crystal‐amorphous interphase. Neat films as well as binary blends with a fullerene derivative are characterized for three different polymers, that are prototypical materials widely used in organic electronics applications. Anisotropic P‐RSoXS patterns reveal two different fibril types. Analysis of theq‐dependence of the anisotropy from simulated and experimental scattering patterns reveal that neat polymer fibrillar systems likely comprise more than two phases, with the third phase in addition to crystal and amorphous likely being an interphase with distinct density and orientation. Intriguingly, the fibril type correlates to the H‐ or J‐aggregation signature in ultraviolet‐visible (UV–vis) spectroscopy, revealing insight into the fibril formation. Together, the results will open the door to develop more sophisticated structure‐function relationships between chemical design, fibril type, formation pathways and kinetics, interfacial ordering, and eventually device functions.

    

   more » « less
5. Experimentally disentangling the influence of dispersal and habitat filtering on benthic invertebrate community structure

   https://doi.org/10.1111/fwb.12995  

   Brown, Bryan L. ; Wahl, Charles ; Swan, Christopher M. ( September 2017 , Freshwater Biology)

   Ecological communities are structured by a combination of local processes like habitat filtering and species interactions, and regional forces driven by the dispersal of organisms between localities on a landscape. Previous studies suggest that the position of local communities within a dispersal network can greatly influence the relative influence of these two sets of processes on community assembly. However, the majority of previous investigations have used models or inferences based on observational data to investigate these hypotheses, while experiments directly addressing this question have been rare.

   We experimentally investigated the relative influence of local and regional processes in structuring benthic invertebrate communities using artificial streams. We manipulated three factors—source pool for the macroinvertebrate community (headwater vs. mainstem) as a surrogate of network location, habitat complexity (high vs. low) in the flume, and dispersal (high vs. low)—and followed changes in macroinvertebrate community structure for 8 weeks.

   Previous research suggests that because headwater (HW) streams are isolated within river networks,HWs are less influenced by regional processes relative to more well‐connected mainstems (MSs). We therefore predicted (i) that flumes colonised from aHWsource community would respond more strongly to our dispersal treatment than those colonised byMScommunities becauseMSwere already largely structured through dispersal‐driven processes, and (ii) that bothHWandMScommunities would respond to manipulations of local habitat, indicating that responses to the dispersal treatment were a direct result of dispersal driven dynamics rather than specific affinity for conditions in the flumes.

   Both of our predictions were strongly supported by the results of the experiment. For flumes withHWsource pools, the high dispersal treatment had significantly higher diversity than low dispersal flumes. However, this difference only occurred in flumes withHWsource pools and did not occur in flumes withMSsources. There was also strong evidence of community composition inHWflumes shifting significantly towards the macroinvertebrate composition in our experimental dispersal treatment. The major effect of experimental dispersal was to introduce new species in fairly low abundances as would be expected from dispersal via drift over a relatively short time. BothMSandHWcolonised flumes showed highly significant signals of habitat filtering, though the influence of specific habitat differed between the source types.

   These results support the hypothesis that dispersal driven processes are a more important structuring force in well‐connected areas of networks by experimentally demonstrating the responsiveness of previously isolated communities to experimentally induced dispersal. They also demonstrate that this responsiveness is not due to an inherent difference in habitat affinity since source communities from bothHWs andMSs responded to manipulation of habitat variables. This experiment only simulated one type of dispersal process in streams—drifting—and did not include simulated dispersal from other sources, nor did it include population dynamics given the relatively short duration of the experiment. Nevertheless, the sensitivity of previously isolated communities to one type of simulated dispersal is a powerful indication of the mechanisms that structure these systems.

    

   more » « less