Millimetre Scale Research Articles

Solid Circulating Velocity Measurement in a Liquid–Solid Micro-Circulating Fluidised Bed

Liquid–solid circulating fluidised beds (CFB) possess many qualities which makes them useful for industrial operations where particle–liquid contact is vital, e.g., improved heat transfer performance, and consequent uniform temperature, limited back mixing, exceptional solid–liquid contact. Despite this, circulating fluidised beds have seen no application in the micro-technology context. Liquid–solid micro circulating fluidised bed (µCFBs), which basically involves micro-particles fluidisation in fluidised beds within the bed of cross-section or inner diameter at the millimetre scale, could find potential applications in the area of micro-process and microfluidics technology. From an engineering standpoint, it is vital to know the solid circulating velocity, since that dictates the bed capability and operability as processing equipment. Albeit there are several studies on solid circulating velocity measurement in CFBs, this article is introducing the first experimental study on solid circulating velocity measurement in a CFB at micro-scale. The experimental studies were done in a novel micro-CFB which was fabricated by micro milling machining 1 mm2 cross-section channels in Perspex and in a 4 mm2 cross-section micro-CFB made by additive manufacturing technology. Soda-lime glass and polymethyl methacrylate (PMMA) micro-particles were employed as solid materials and tap water as the liquid medium. The digital particle image velocimetry (PIV) method was used as a measurement technique to determine the particle velocity in the micro-CFB system and validated by the valve accumulation technique using a novel magnetic micro-valve. The measured critical transition velocity, Ucr, is comparable to the particle terminal velocity, i.e., the normalised transition velocity is approximately 1 in line with macroscopic systems results and our previous study using simple visual observation. As in macroscopic CFB systems, Ucr decreased with solid inventory (1–9%) and finally becomes stable when the solid inventory is high enough (10–25%) and it increases with a reduction in particle size and density.

Tunable flow asymmetry and flow rectification with bio-inspired soft leaflets

In Nature, liquids often circulate in channels textured with leaflets, cilia or porous walls that deform with the flow. These soft structures are optimized to passively control flows and inspire the design of novel microfluidic and soft robotic devices. Yet so far the relationship between the geometry of the soft structures and the properties of the flow remains poorly understood. Here, taking inspiration from the lymphatic system, we devise millimetric scale fluidic channels with asymmetric soft leaflets that passively increase (reduce) the channel resistance for forward (backward) flows. Combining experiments, numerics and analytical theory, we show that tuning the geometry of the leaflets controls the flow properties of the channel through an interplay between asymmetry and nonlinearity. In particular, we find the conditions for which flow asymmetry is maximal. Our results open the way to a better characterization of biological leaflet malformations and to more accurate control of flow orientation and pumping mechanisms for microfluidics and soft robotic systems.

Evaluation of a 12-week allopurinol-lowering therapy in combination with the non-steroidal anti-inflammatory drug meloxicam in patients with gout

To evaluate a 12-week course of combined alloturinol-lowering therapy with a prophylactic anti-inflammatory dose of movalis for the frequency of exacerbations and the quality of life of patients with gout. Allopurinol was administered orally, 1 time per day. Every 3 weeks, the dosage of the drug was increased by 50 mg to 300 mg per day under the control of the level of serum uric acid (sUA). The total daily dose of the drug movalis, used in the form of different dosage forms, was 7.515 mg. The clinical effectiveness of the treatment was evaluated after 3, 6, 9 and 12 weeks according to physical examination, the dynamics of joint pain at rest, during movement and palpation, according to the visual analogue scale (VAS) in millimeters, Likert scale, EuroQol-5D-5L questionnaire, care for oneself, habitual daily activities, the presence of anxiety and depression, assessment of satisfaction with treatment (on a scale of 1 to 5, where 1 is the complete absence of improvement or worsening, and 5 is a very good result); took into account the period of remission, as well as the time before the onset of relapse of gouty arthritis. An adverse event (AE) was recorded. On the background of treatment with movalis 7.5 mg per day more than two-thirds of patients showed no worsening of the articular syndrome with an increase in the dose of allopurinol to 300 mg per day. By the 12th week of observation, a significant difference was found between the severity of gouty arthritis characteristics in the direction of improving mobility, self-care, normal daily activities, reducing soreness, reducing anxiety and depression (p0.05). In addition, the ESR and sUA levels were significantly different initially and at the final observation point (p0.05), which indicates a positive effect on the inflammatory process. A 3-month course of combination therapy was not accompanied by significant increases in blood pressure, changes in creatinine clearance in blood serum. There were no adverse events from the gastrointestinal tract. 90.9% of patients rated the treatment result as very good. AE in the form of a skin allergic rash was observed in one patient; it did not require interruption of treatment and completely stopped without consequences after completion of the course. 12 a week-long combined therapy of the allopurinol-reducing drug with the anti-inflammatory dose movalis prevents the exacerbation of the articular syndrome and improves the quality of life of patients with gout.

Two-step method of nanosecond pulse laser ablation manufacturing of miniature bevel line gears

Miniature gears have important research value and application prospects in micro-scale machinery. The existing manufacturing methods for miniature gears produce spur gears on the micron scale and spur, helical and bevel gears on the millimetre scale. However, there is no mature process for gears on the micron scale for angular transmissions, such as bevel gears. This article reports for the first time the micro-machining of a miniature bevel gear with an external size of 1–2 mm based on a novel gear structure: the bevel line gear. First, a novel manufacturing method, namely the two-step method of nanosecond pulse laser ablation (NSPLA), is proposed. Then, a sample of a miniature bevel line gear is fabricated from 6061 aluminium alloy with a top angle of 90°, external diameter of 1375 μm, tooth number of 3 and average tooth width of 20 μm. Finally, the accuracy of the sample is studied to confirm the practicability of the proposed method.

Motion corrected MRI differentiates male and female human brain growth trajectories from mid-gestation

It is of considerable scientific, medical, and societal interest to understand the developmental origins of differences between male and female brains. Here we report the use of advances in MR imaging and analysis to accurately measure global, lobe and millimetre scale growth trajectory patterns over 18 gestational weeks in normal pregnancies with repeated measures. Statistical modelling of absolute growth trajectories revealed underlying differences in many measures, potentially reflecting overall body size differences. However, models of relative growth accounting for global measures revealed a complex temporal form, with strikingly similar cortical development in males and females at lobe scales. In contrast, local cortical growth patterns and larger scale white matter volume and surface measures differed significantly between male and female. Many proportional differences were maintained during neurogenesis and over 18 weeks of growth. These indicate sex related sculpting of neuroanatomy begins early in development, before cortical folding, potentially influencing postnatal development.

Development of gateless quantum Hall checkerboard p–n junction devices

Measurements of fractional multiples of the plateau quantized Hall resistance ( ≈ 12 906 Ω) were enabled by the utilization of multiple current terminals on millimetre-scale graphene p–n junction (pnJ) devices fabricated with interfaces along both lateral directions. These quantum Hall resistance checkerboard devices have been demonstrated to match quantized resistance outputs numerically calculated with the LTspice circuit simulator. From the devices’ functionality, more complex embodiments of the quantum Hall resistance checkerboard were simulated to highlight the parameter space within which these devices could operate. Moreover, these measurements suggest that the scalability of pnJ fabrication on millimetre or centimetre scales is feasible with regards to graphene device manufacturing by using the far more efficient process of standard ultraviolet lithography.

Investigation of nano-microstructural changes in Maastricht limestone after treatment with nanolime suspension

Nanolimes are dispersions of nanosized Ca(OH)2 particles in alcohols often used for the consolidation of various types of cultural heritage objects. The consolidation effect is based on the transformation of Ca(OH)2 into CaCO3 phases during carbonation process. The detection of microstructural changes consequent to a consolidating treatment (essential to evaluate its effectiveness) was approached adopting the innovative combination of two advanced techniques, covering a range in pore size from the nanometric to the millimetric scale: small-angle neutron scattering (SANS) and synchrotron X-ray micro-computed tomography (µ-CT). The changes in the 3D microstructure of samples of Maastricht limestone, a well-known weak stone material considered as a sort of ‘standard’ in cultural heritage conservation studies, pure and treated with nanolime dispersions, have been described in a fully non-invasive fashion, overcoming the limitation of previous approaches. The application of nanolime resulted to have a limited positive effect in reducing the fine porosity. Its time evolution was attributed to the progress of the carbonation reaction. On the contrary, the treatment produced positive effects on the porosity in the size range covered with µ-CT, reducing the pore accessibility between 30 and 65 µm, suggesting an improvement of the mechanical properties. The combined use of SANS and µ-CT represents and novel methodological approach in support of cultural heritage conservation works.

Early diagenetic pyrite cementation influences molecular composition of sedimentary organic matter in the Dongying Depression, China

Micro-variations of lipid hydrocarbons and biomarkers in well-laminated shales have not been extensively documented, especially within different rock textures, fabrics and mineralogies. Comparison of a pyrite cemented zone and its surrounding sediment may offer a new perspective on mineral control on preservation of hydrocarbons and organic carbon. A black well-laminated shale comprising two adjacent and contrasting calcareous (light) and pyrite (dark) laminae at the millimetre scale was selected from the Eocene Shahejie Formation, Dongying Depression, Bohai Bay Basin. It was horizontally sliced to separate a pyrite cemented concretion from the unaltered laminated shale, and investigated using geochemical techniques to assess the heterogeneity of elements, minerals, microfossils and hydrocarbons within the two slices. Micro-scale changes in source inputs were noted. For instance, the 4α-methylsteranes, dinosteranes and the triaromatic dinosteranes show varying distributions between the two slices, attributed to slight differences in dinoflagellate contributions. Similarly, variation in the amount of bacterial sulfate reduction is indicated by variations in the aryl isoprenoid ratio, relative amount of isorenieratane, long-chain n-alkane carbon isotopic composition and other molecular indicators including the relative amounts of dibenzothiophene, dibenzofuran, methyldibenzothiophene and methyltrimethyltridecylchromans. The primary control on these variations appears to be different euxinic water conditions, but diagenesis has also influenced the distributions. Differential anaerobic bacterial reworking of organic matter and pyrite concretion protection are responsible for organic geochemical variations on a millimetre-scale in the shale. The pyrite concretion has an altered record of its thermal history, but has a more accurate record of the organic geochemistry of microfossils and water column conditions. This study shows the potential for future investigations of closely-spaced vertical variation in organic geochemical parameters that may shed light on rapid temporal variation in organic matter input and depositional environment.

High-resolution distributed vertical strain and velocity from repeat borehole logging by optical televiewer: Derwael Ice Rise, Antarctica

AbstractDirect measurements of spatially distributed vertical strain within ice masses are scientifically valuable but challenging to acquire. We use manual marker tracking and automatic cross correlation between two repeat optical televiewer (OPTV) images of an ~100 m-long borehole at Derwael Ice Rise (DIR), Antarctica, to reconstruct discretised, vertical strain rate and velocity at millimetre resolution. The resulting profiles decay with depth, from −0.07 a−1at the surface to ~−0.002 a−1towards the base in strain and from −1.3 m a−1at the surface to ~−0.5 m a−1towards the base in velocity. Both profiles also show substantial local variability. Three coffee-can markers installed at different depths into adjacent boreholes record consistent strain rates and velocities, although averaged over longer depth ranges and subject to greater uncertainty. Measured strain-rate profiles generally compare closely with output from a 2-D ice-flow model, while the former additionally reveal substantial high-resolution variability. We conclude that repeat OPTV borehole logging represents an effective means of measuring distributed vertical strain at millimetre scale, revealing high-resolution variability along the uppermost ~100 m of DIR, Antarctica.

Abstract QS36: Spatial Fidelity Of Microvascular Perforating Vessels As Perceived By Augmented Reality Holographic Projections

Purpose: Breast reconstruction using free-tissue transfer yields improved long-term aesthetic results as reported by patients, but requires increased resources of practitioners and hospital systems. Much of the complexity of microvascular reconstruction can be attributed to flap harvest, as dissection must account for anatomic variability, and is guided at best by ancillary imaging modalities which must be extrapolated to the patient on the table. Augmented reality affords the opportunity to superimpose relevant imaging on a surgeon’s native field of view. This potentially allows integration of imaging in real-time to better guide flap selection and facilitate dissection. We aimed to assess the spatial fidelity of key anatomic landmarks on augmented-reality projections compared to 3D printed anatomic simulacrum models formatted from CT-Angiography (CTA) imaging in patients undergoing autologous breast reconstruction. Methods: 3D-printed composite models of rectus abdominal muscles and associated Deep Inferior Epigastric Arteries (DIEP) with perforating vessels were fabricated from CTA data from de-identified patients. The corresponding CTA data was similarly formatted to be used on the Microsoft Hololens with the Microsoft Mixed Reality Toolkit 2.01 and Unity 2019.2.4 Visual Studio. Coordinates were measured using the OptiTrack Flex 13 Motion tracking system. The 3D printed models were zeroed to an arbitrary reference point maintained for each set specimen. Established anatomic points including upper and lower borders of the umbilicus, superficial location of perforating vessels, and corners of the model were initially measured. The Hololens projection was then superimposed using hand-gesture and voice commands onto the model, and set into place, ensuring immobile position despite translational movement of the headset. The model was then removed, and the corresponding anatomic reference points were recorded in triplicate from two separate vantages. Results: Five sets of 3D printed models and corresponding Hololens projections were measured. Absolute distance from left to right perforators were calculated from measurements of the model and the Hololens projection, from two vantages. Analysis of variance (ANOVA) were conducted on each group of measurements independently for each specimen. In two of the five specimens (#1 and #32), there was no significant difference in inter-perforator distance. The greatest discrepancy of inter-perforator distance between any projection and those measured on 3D models was 5.6 mm in specimen 21. Conclusions: Our data demonstrate that holographic projections can be used to accurately localize relevant three-dimensional structures extrapolated from CT imaging, on the scale of millimeters. Two of five models demonstrated no significant variability in perceived three-dimensional location of inter-perforator distance and, despite significant inter-group variability, Hololens projections were perceived within millimeters of the corresponding physical landmark. Augmented reality provides a potential paradigm shifting adjunct for intra-operative localization of perforating vessels in free-tissue flap harvest.

Application of polymer dose gels for millimeter scale target/tumor pre-treatment immitation using gamma knife facility

Polymer gels are widely used for absorbed dose verification in radiotherapy, providing information about 3D dose distribution in the irradiated volume as well as serving as a simulation phantom, for the observation of radiation induced structural changes, related to gel’s polymerization upon irradiation. Due to high spatial resolution and unable sensitivity through gel’s composition, dosimeter gels is a powerful and precise tool for verification of individual treatment plans especially when high treatment doses are prescribed.The aim of this work was to modify and characterize gel dosimeters that are capable of millimetre scale target/tumour imitation and high dose assessment in small irradiated volume, for their further applications in clinical dosimetry and verification of millimetre scale target treatment procedures using Gamma knife unit.

Imaging of boron distribution in steel with neutron radiography and tomography

B distribution in steel was investigated using neutron imaging techniques, on a millimetric scale with a spatial resolution below 100 μm. Steel structural components joined using the transient liquid-phase bonding (TLPB) process, with Fe-based B-alloyed foils as filler material, were observed. By means of neutron radiography and with the proposed calibration method, a quantitative profile of B concentration was attained across the joint, in particular in the region where the completion of the TLPB process was achieved. It is noteworthy that B concentration did not exceed the typical specified range of B-alloyed steels. This result explains why prior austenite grain boundaries are boride-free. To test the validity of the measured B concentrations, they were compared with those of the numerically simulated TLPB process. As a result, the calculated and experimentally measured values are in good agreement, within the estimated error. On the other hand, in regions where the TLPB process was not finished, athermally solidified liquid (ASL) was found at the joint, in the form of borides. In addition, neutron tomography enabled us to attain a three-dimensional visualization of the size and distribution of ASL, highlighting its potential as a non-destructive testing technique of TLPB weldments.

Spatially dependent kinetics of helium in tungsten under fusion conditions

Tungsten is the prime candidate material for divertor applications in future nuclear reactors (e.g. ITER and DEMO). In the present work, a spatially dependent cluster dynamics model is developed to investigate and understand the microstructure evolution of tungsten under low energy helium implantation and neutron irradiation varying over bulk length scales of millimetres and irradiation time scales of hours. The diffusion of helium, helium clusters and their trapping at neutron induced defects is simulated along the tungsten monoblock depth. The temperature gradient resulting from a steady state heat load of 10 MWm−2 along the monoblock depth is considered and its influence on the evolution of defects is discussed. The trapping of helium at vacancies and the associated formation of helium-vacancy clusters is found to be pronounced in the sub-surface layers. A significant influence of helium detrapping from grain boundaries and dislocations, along with its resolution from clusters, on the helium diffusion length scales is observed. Additionally, the effect of helium cluster mobility is investigated and overall lower retention in the monoblock bulk is observed through significant release of helium at the surface.

Visualization of Carrier Transport in Luminescent Polymer Thin Film by Using Transient Photoluminescence Decay Imaging

Transient photoluminescence (PL) decay imaging is conducted for visualizing carrier transport in luminescent polymer semiconductor thin films. The method is simple, but enables a real‐time observation of carrier motion on the scale of several millimeters in luminescent thin films. Decrease in the PL intensity of the channel region in organic field‐effect transistor (OFET) is observed in accordance with the device operation. Upon application of pulse voltages to the source electrode for carrier injection, the transient PL decay motion is visualized using a conventional charge‐coupled device (CCD) camera. By analyzing the PL decay motion, hole and electron mobilities of poly(9,9‐di‐n‐octylfluorene‐alt‐benzothiadiazole) (F8BT) thin film are evaluated as 1.3 × 10−4 cm2 (V s)−1 and 3.2 × 10−5 cm2 (V s)−1, respectively. Mobility anisotropy is also visualized by using round‐shaped electrode as the source electrode, and the difference of mobility anisotropy for hole and electron of F8BT is clearly identified.

Temporal and spatial evolution of soil surface roughness on stony plots

Soil surface roughness (SSR) is widely recognized as an important factor influencing water erosion processes. On semiarid hillslopes with stony soils, rock fragments accumulate as the result of preferential erosion of fine materials, often creating a rough, rocky surface. A series of rainfall events were simulated on a stony plot (2 × 6.1 m) at three slope gradients (5 %, 12 %, and 20 %) and rock cover was measured. Surface elevations were sampled by terrestrial LiDAR at high resolutions. Roughness indices, including random roughness (RR), fractal dimension, crossover length, and generalized fractal dimension, were calculated from LiDAR points directly. Results showed: 1) SSR displayed an increasing trend as the rainfall simulation proceeded for all three slope treatments; 2) the steeper slope developed greater surface roughness; and 3) both the increase of surficial exposed rocks and the formation of erosional features, e.g., rills and depressions, contributed to the spatiotemporal variations of SSR. Results also showed that the fractal dimension was not a good indicator of soil surface roughness, but rather was an index of the form of the surface. Crossover length was a measure of roughness at a scale of a few millimeters, while random roughness was a measure of elevation variations on the scale of the length of the transect measured, and thus encompassed larger morphological features including rills. We also established a new method for multifractal analysis that characterized the heterogeneity of soil surface roughness. These results improve our understanding of the evolution of semiarid stony hillslopes and the dynamic feedback mechanism between erosion, surface morphology and hydraulics.

Thermal Localization Enhanced Fast Photothermoelectric Response in a Quasi-One-Dimensional Flexible NbS3 Photodetector.

Ultra-broadband photodetection is crucial for various applications like imaging and sensing and has become a hot research topic in recent years. However, most of the reported ultra-broadband photodetectors can only cover the range from ultraviolet to infrared, which is insufficient. Herein, a photothermoelectric (PTE) detector made of NbS3 is reported. The device shows a considerable performance from ultraviolet to terahertz. For all examined wavelengths, the photoresponsivities are all larger than 1 V W-1 while the response time is less than 10 ms, much shorter than the reported ultra-broadband photodetectors made of millimetric scale graphene, ternary chalcogenide single crystal, and other materials. The extraordinary performance is fully discussed and can be attributed to the thermal localization enhanced PTE effect. Because of the short thermal decay length and low thermal loss, the heat generated by the illumination is localized in only a micrometer scale along the channel, and thus a strong PTE response is produced. In addition, the fabricated device also demonstrates robust flexibility and stability. Thanks to the quasi-one-dimensional (quasi-1D) structure, the NbS3 crystal is easy to be scaled down and thus intrinsically facilitate the integration of detectors. With these favorable merits, the quasi-1D NbS3 crystal holds a promising potential in high-performance, ultra-broadband photodetectors.

Non-Destructive Investigation of Dispersion, Bonding, and Thermal Properties of Emerging Polymer Nanocomposites Using Close-Up Lens Assisted Infrared Thermography

AbstractPolymer nanocomposites possess unique sets of properties that make them suitable for different applications, including structural and flame-retardant material, electromagnetic wave reflector, sensors, thin film transistor, flexible display, and many more. The properties of these nanocomposite are dependent on nanofiller dispersion and bonding with polymer matrix (i.e. particle-matrix interaction). Thermography is a non-destructive method that may be used to gain insight into dispersion and particle-matrix interaction. Infrared (IR) radiation emitted from these nanomaterial polymer composite depends on the emissivity of the individual components. In addition, during flash heating and cooling, different thermal conductivity of components in the nanocomposite can influence pixel intensity differently in the IR image or video being captured. We have used an economical mid wavelength IR camera Fluke RSE600 equipped with a close-up macro lens and algorithm based on MATLAB image processing toolbox to analyse dispersion, voids and thermal diffusivity of patented graphene polymer nanocomposite materials (G-PMC) in micro-scale. These G-PMCs can act as a standard material to determine the potential of our IR thermography technique due to their homogeneity and lack of impurity due to unique fabrication process. Thermal diffusivity and dispersion of nanoparticles in our G-PMCs was estimated after irradiation with a xenon flash lamp by spatially mapping transient IR radiations from different G-PMCs using the Fluke RSE600 thermal imager. Results from thermography experiments were compared with scanning electron microscope (SEM) and Raman spectroscopy results. Micro-scale thermography was able to detect millimetre scale thermal diffusivity variation in the injection molded G-PMC samples and relate it to change in dispersion of nanofillers, unlike SEM and Raman, where micro-scale measurements could not determine the reason behind millimetre scale property variation. We believe this low cost, fast, micro-scale, non-destructive technique will provide valuable insight into functional polymer nanocomposite fabrication and corresponding electrical and thermal properties.

Sustainability of spatially distributed bacteria-phage systems

Virulent phages can expose their bacterial hosts to devastating epidemics, in principle leading to complete elimination of their hosts. Although experiments indeed confirm a large reduction of susceptible bacteria, there are no reports of complete extinctions. We here address this phenomenon from the perspective of spatial organization of bacteria and how this can influence the final survival of them. By modelling the transient dynamics of bacteria and phages when they are introduced into an environment with finite resources, we quantify how time delayed lysis, the spatial separation of initial bacterial positions, and the self-protection of bacteria growing in spherical colonies favour bacterial survival. Our results suggest that spatial structures on the millimetre and submillimetre scale play an important role in maintaining microbial diversity.

Proton deflectometry of a capacitor coil target along two axes

A developing application of laser-driven currents is the generation of magnetic fields of picosecond–nanosecond duration with magnitudes exceeding $B=10~\text{T}$ . Single-loop and helical coil targets can direct laser-driven discharge currents along wires to generate spatially uniform, quasi-static magnetic fields on the millimetre scale. Here, we present proton deflectometry across two axes of a single-loop coil ranging from 1 to 2 mm in diameter. Comparison with proton tracking simulations shows that measured magnetic fields are the result of kiloampere currents in the coil and electric charges distributed around the coil target. Using this dual-axis platform for proton deflectometry, robust measurements can be made of the evolution of magnetic fields in a capacitor coil target.

Reorganization of complex ciliary flows around regenerating Stentor coeruleus.

The phenomenon of ciliary coordination has garnered increasing attention in recent decades and multiple theories have been proposed to explain its occurrence in different biological systems. While hydrodynamic interactions are thought to dictate the large-scale coordinated activity of epithelial cilia for fluid transport, it is rather basal coupling that accounts for synchronous swimming gaits in model microeukaryotes such as Chlamydomonas. Unicellular ciliates present a fascinating yet understudied context in which coordination is found to persist in ciliary arrays positioned across millimetre scales on the same cell. Here, we focus on the ciliate Stentor coeruleus, chosen for its large size, complex ciliary organization, and capacity for cellular regeneration. These large protists exhibit ciliary differentiation between cortical rows of short body cilia used for swimming, and an anterior ring of longer, fused cilia called the membranellar band (MB). The oral cilia in the MB beat metachronously to produce strong feeding currents. Remarkably, upon injury, the MB can be shed and regenerated de novo. Here, we follow and track this developmental sequence in its entirety to elucidate the emergence of coordinated ciliary beating: from band formation, elongation, curling and final migration towards the cell anterior. We reveal a complex interplay between hydrodynamics and ciliary restructuring in Stentor, and highlight for the first time the importance of a ring-like topology for achieving long-range metachronism in ciliated structures.This article is part of the Theo Murphy meeting issue ‘Unity and diversity of cilia in locomotion and transport’.