Journal articles: 'Curvature driven migration'

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Martorano, M. A., M. A. Fortes, and A. F. Padilha. "A numerical method for curvature driven boundary migration." Modelling and Simulation in Materials Science and Engineering 14, no. 1 (January 1, 2006): 83–98. http://dx.doi.org/10.1088/0965-0393/14/1/007.

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Li, Ningwei, Nima Sharifi-Mood, Fuquan Tu, Daeyeon Lee, Ravi Radhakrishnan, Tobias Baumgart, and Kathleen J. Stebe. "Curvature-Driven Migration of Colloids on Tense Lipid Bilayers." Langmuir 33, no. 2 (December 30, 2016): 600–610. http://dx.doi.org/10.1021/acs.langmuir.6b03406.

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Cavallaro, M., L. Botto, E. P. Lewandowski, M. Wang, and K. J. Stebe. "Curvature-driven capillary migration and assembly of rod-like particles." Proceedings of the National Academy of Sciences 108, no. 52 (December 19, 2011): 20923–28. http://dx.doi.org/10.1073/pnas.1116344108.

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Zhang, H., M. Upmanyu, and D. J. Srolovitz. "Curvature driven grain boundary migration in aluminum: molecular dynamics simulations." Acta Materialia 53, no. 1 (January 2005): 79–86. http://dx.doi.org/10.1016/j.actamat.2004.09.004.

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Ask, Anna, Samuel Forest, Benoit Appolaire, and Kais Ammar. "Cosserat crystal plasticity with dislocation-driven grain boundary migration." Journal of Micromechanics and Molecular Physics 03, no. 03n04 (September 2018): 1840009. http://dx.doi.org/10.1142/s242491301840009x.

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This paper discusses a coupled mechanics–phase-field model that can predict microstructure evolution in metallic polycrystals and in particular evolution of lattice orientation due to either deformation or grain boundary migration. The modeling framework relies on the link between lattice curvature and geometrically necessary dislocations and connects a micropolar or Cosserat theory with an orientation phase-field model. Some focus is placed on the underlying theory and in particular the theory of dislocations within a continuum single crystal plasticity setting. The model is finally applied to the triple junction problem for which there is an analytic solution if the grain boundary energies are known. The attention is drawn on the evolution of skew–symmetric stresses inside the grain boundary during migration.

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Morawiec, A. "On 2D interface networks that are translation-invariant under curvature-driven migration." Modelling and Simulation in Materials Science and Engineering 27, no. 1 (December 10, 2018): 015003. http://dx.doi.org/10.1088/1361-651x/aaef1a.

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Kim, Dong-Kyu, Ho Won Lee, Kyung-Hwan Jung, and Yong-Taek Im. "Mesoscopic Modeling of Primary Recrystallization of AA1050 with Curvature-Driven Interface Migration Effect." MATERIALS TRANSACTIONS 54, no. 1 (2013): 81–89. http://dx.doi.org/10.2320/matertrans.m2012267.

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Talbot, Emma L., Lucia Parolini, Jurij Kotar, Lorenzo Di Michele, and Pietro Cicuta. "Thermal-driven domain and cargo transport in lipid membranes." Proceedings of the National Academy of Sciences 114, no. 5 (January 17, 2017): 846–51. http://dx.doi.org/10.1073/pnas.1613525114.

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Domain migration is observed on the surface of ternary giant unilamellar vesicles held in a temperature gradient in conditions where they exhibit coexistence of two liquid phases. The migration localizes domains to the hot side of the vesicle, regardless of whether the domain is composed of the more ordered or disordered phase and regardless of the proximity to chamber boundaries. The distribution of domains is explored for domains that coarsen and for those held apart due to long-range repulsions. After considering several potential mechanisms for the migration, including the temperature preferences for each lipid, the favored curvature for each phase, and the thermophoretic flow around the vesicle, we show that observations are consistent with the general process of minimizing the system’s line tension energy, because of the lowering of line interface energy closer to mixing. DNA strands, attached to the lipid bilayer with cholesterol anchors, act as an exemplar “cargo,” demonstrating that the directed motion of domains toward higher temperatures provides a route to relocate species that preferentially reside in the domains.

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Sheikh-Ali, A. D. "The effect of grain boundary sliding on curvature-driven boundary migration in Zn bicrystals." Scripta Materialia 56, no. 12 (June 2007): 1043–46. http://dx.doi.org/10.1016/j.scriptamat.2007.02.031.

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Maazi, N., and R. Penelle. "Modeling of the Particles Pinning Effect on Grain Growth." Materials Science Forum 702-703 (December 2011): 599–602. http://dx.doi.org/10.4028/www.scientific.net/msf.702-703.599.

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In silicon steels, interaction of grain boundaries with particles occurs in a selective way. Currently, it is very difficult to include this preferential interaction directly in the classical simulation models. A new approach of grain growth simulation based on the concept of curvature-driven migration of the grain boundaries in the presence of particles has been used to study the abnormal grain growth (AGG) in Fe-3%Si alloy.

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Kim, Dong Kyu, K. H. Jung, H. W. Lee, and Yong Taek Im. "Cellular Automata Simulation of Textural Evolution during Primary Static Recrystallization of IF Steel." Materials Science Forum 702-703 (December 2011): 615–18. http://dx.doi.org/10.4028/www.scientific.net/msf.702-703.615.

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A two dimensional probabilistic cellular automata model is used to simulate primary static recrystallization of interstitial free (IF) steel. The present study is to investigate the effect of curvature-driven pressure that is induced by protrusions/retrusions of recrystallization fronts on the microstructural and textural evolution during recrystallization. It was found that local interface migration of protrusions/retrusions of recrystallization fronts could significantly affect the kinetics, grain morphology and annealing texture according to the present investigation.

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Molodov, Dmitri A. "Grain Boundary Dynamics in High Magnetic Fields. Fundamentals and Implications for Materials Processing." Materials Science Forum 467-470 (October 2004): 697–706. http://dx.doi.org/10.4028/www.scientific.net/msf.467-470.697.

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The latest research on dynamics of grain boundaries in non-magnetic materials in high magnetic fields is reviewed. A control of grain boundary migration means control of microstructure evolution, which is a key for the design of materials with desire properties. Grain boundary motion can be affected by a magnetic field, if the anisotropy of the magnetic susceptibility generates a gradient of the magnetic free energy. In contrast to curvature driven boundary motion, a magnetic driving force also acts on planar boundaries so that the motion of crystallographically well-defined boundaries can be investigated, and the true grain boundary mobility can be determined. The results of migration measurements obtained on bismuth and zinc bicrystals are addressed. Selective growth of new grains in locally deformed zinc single crystals driven by a magnetic force is reported as well. Implications for materials processing, in particular the effect of magnetic fields on texture development in hcp metals are finally discussed.

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Taheri, M. L., D. Molodov, G. Gottstein, and A. D. Rollett. "Grain boundary mobility under a stored-energy driving force: a comparison to curvature-driven boundary migration." Zeitschrift für Metallkunde 96, no. 10 (October 2005): 1166–70. http://dx.doi.org/10.3139/146.101157.

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Taheri, M. L., D. Molodov, G. Gottstein, and A. D. Rollett. "Grain boundary mobility under a stored-energy driving force: a comparison to curvature-driven boundary migration." International Journal of Materials Research 96, no. 10 (October 1, 2005): 1166–70. http://dx.doi.org/10.1515/ijmr-2005-0201.

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Abstract Grain boundary mobility has been measured in high-purity aluminum alloyed with 0.03 wt.% Zr using energy stored during plastic deformation as a driving force. In general, the dependence of mobility on grain boundary character was similar to that observed by previous authors with a maximum in mobility in the vicinity of the ∑7 type (38°<111>). The exact location of the mobility maximum varied, however, with temperature in a manner similar to that observed for curvature-driven mobility measurements. Although <111> tilt boundaries exhibit high mobilities in general, the single peak at the ∑7 position at low temperatures changes to a double peak at high temperatures with a local minimum at ∑7. The combination of mobility variation and the thermal activation analysis of the results points to a compensation temperature effect. All these results suggest that grain boundary mobility is a true material property.

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Montheillet, Frank, and David Piot. "Combined Effects of Grain Boundary Convection and Migration in Dynamic Phase Transformations." Materials Science Forum 879 (November 2016): 72–77. http://dx.doi.org/10.4028/www.scientific.net/msf.879.72.

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During large strain deformation of polycrystals, grain or interphase boundaries are driven by the material flow, which is a convection movement. By contrast, upon static recrystallization or grain growth, their motion takes place with respect to matter, which is referred to as grain boundary or interphase migration. During hot working, where dynamic phase transformations commonly occur, convection and migration operate simultaneously. According to local geometrical (e.g., prescribed velocity field, grain boundary curvature) and physical (e.g., grain boundary mobility, dislocation densities) conditions, they can reinforce or oppose each other, but generally combine in more complex ways. The aim of this work is to analyze such effects on the basis of simple analytical approaches. The results suggest that second phase particles or grains dynamically generated (i.e., during straining) exhibit approximately equiaxed shapes.

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Tikare, Veena, Michael V. Braginsky, Didier Bouvard, and Alexander Vagnon. "An Experimental Validation of a 3D Kinetic, Monte Carlo Model for Microstructural Evolution during Sintering." Advances in Science and Technology 45 (October 2006): 522–29. http://dx.doi.org/10.4028/www.scientific.net/ast.45.522.

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An experimental validation of a 3D kinetic, Monte Carlo model for simulation of microstructural evolution during solid state sintering will be presented. The model – a statistical mechanical model, which can simulate curvature-driven grain growth, pore migration, and vacancy formation, diffusion and annihilation – is validated by comparing microstructural evolution obtained experimentally for a copper powder compact. The 3D microstructural evolution of copper powder particles sintering was imaged in-situ by microtomography. The images show particles with internal porosity percolating through the particles. Microstructural features – e.g., neck formation and growth – from the experimental images as well as the overall densification rates are compared to the simulations.

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Zhang, Zi-Yue. "Molecular dynamics studies on the grain growth of nanocrystalline Ni and Ni3Al." Modern Physics Letters B 31, no. 26 (September 20, 2017): 1750237. http://dx.doi.org/10.1142/s0217984917502372.

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With molecular dynamics simulations, the growth of face-centered-cubic nanocrystalline materials Ni and Ni3Al has been studied. It is found that grain-rotation induced grain coalescence and curvature-driven grain-boundary migration are dominant mechanisms in the nanograin growth. A detailed comparison of the nanograin growth between the two systems is discussed in terms of grain rotation and grain sliding. We also study the temperature effect and the size effect in the nanograin growth. The tendency of twinning in the nanograin growth is discussed. It is found that in Ni3Al, it seems more possible for nanograins to grow into twin-like structures than single crystal unless at very high temperatures.

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Molodov, Dmitri A. "Motion of Grain Boundaries: Experiments on Bicrystals." Diffusion Foundations 5 (July 2015): 247–71. http://dx.doi.org/10.4028/www.scientific.net/df.5.247.

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Recent research on grain boundary migration is reviewed. Novel in-situ measuring techniques based on orientation contrast imaging and the experimental results obtained on specially grown bicrystals are presented. Particularly, the investigated faceting and migration behavior of low angle grain boundaries under the curvature force in aluminum bicrystals was addressed. In contrast to the pure tilt boundaries, which remained straight/flat and immobile during annealing at elevated temperatures, mixed tilt-twist boundaries readily assumed a curved shape and steadily moved under the capillary force. Computational analysis revealed that this behavior is due to the inclinational anisotropy of grain boundary energy, which in turn depends on boundary geometry. The migration of planar grain boundaries induced by a magnetic field was measured in bismuth and zinc bicrystals. Various structurally different boundaries were investigated. The results revealed that grain boundary mobility essentially depends on the misorientation angle and the inclination of the boundary plane. Stress driven boundary migration in aluminium bicrystals was observed to be coupled to a tangential translation of the grains. The activation enthalpy of high angle boundary migration was found to vary non-monotonously with misorientation angle, whereas for low angle boundaries the migration activation enthalpy was virtually the same. The motion of the mixed tilt-twist boundaries under stress was observed to be accompanied by both the translation of adjacent grains parallel to the boundary plane and their rotation around the boundary plane normal.

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Maazi, N., N. Rouag, and Richard Penelle. "Comparison of the Morphological Effect for the Simulation of Abnormal Goss Grain Growth in Two Fe-3%Si Alloys, Grades Hi-B and CGO." Materials Science Forum 467-470 (October 2004): 887–92. http://dx.doi.org/10.4028/www.scientific.net/msf.467-470.887.

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A grain growth simulation based on the concept of grain boundary migration driven by the radius curvature has been tested to study the abnormal grain growth (AGG) of the Goss grains in silicon steels in presence of particles. In the classical simulation of AGG, the grain size is generally assumed to be homogeneous. In order to introduce the influence of the morphological and crystallographic heterogeneities on AGG around the Goss grain, the simulation procedure has been implemented using as starting state an experimental microstructure characterized by Orientation Imaging Microscopy (OIMTM). Abnormal growth results are compared for the two grades, Hi-B and CGO of Fe-3%Si alloys. It has been notably shown that the large grains resist AGG so that the Goss grain shape becomes anisotropic.

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Daniels, Patrick, Jon Ihlefeld, William Borland, and Jon-Paul Maria. "Smart electrodes for ultralarge-area thin film capacitors." Journal of Materials Research 22, no. 7 (July 2007): 1763–66. http://dx.doi.org/10.1557/jmr.2007.0272.

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A process suitable for preparing metal-insulator-metal thin film capacitors with submicron insulating layers and top electrodes with cm-scale dimensions is presented. Most importantly, this process does not require sophisticated deposition equipment or a clean room environment. The key to large area yield is co-firing the insulator film with a non-dewetting electrode during the dielectric crystallization/densification anneal. We propose a mechanism of electrode dewetting during the high temperature anneal where the metal laterally retreats from geometric asperities that compromise the integrity of the insulating layer. This behavior is driven by surface energy minimization, which promotes metal migration away from the regions of high curvature. This methodology is not material specific, and only requires a top electrode with a large contact angle to the dielectric in question. Using this technique, functional thin film capacitors with 2.5 cm lateral dimensions and 1 μm dielectric thicknesses can be routinely prepared.

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Duruk, Selin, Edouard Boujo, and Mathieu Sellier. "Thin Liquid Film Dynamics on a Spinning Spheroid." Fluids 6, no. 9 (September 6, 2021): 318. http://dx.doi.org/10.3390/fluids6090318.

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The present work explores the impact of rotation on the dynamics of a thin liquid layer deposited on a spheroid (bi-axial ellipsoid) rotating around its vertical axis. An evolution equation based on the lubrication approximation was derived, which takes into account the combined effects of the non-uniform curvature, capillarity, gravity, and rotation. This approximate model was solved numerically, and the results were compared favorably with solutions of the full Navier–Stokes equations. A key advantage of the lubrication approximation is the solution time, which was shown to be at least one order of magnitude shorter than for the full Navier–Stokes equations, revealing the prospect of controlling film dynamics for coating applications. The thin film dynamics were investigated for a wide range of geometric, kinematic, and material parameters. The model showed that, in contrast to the purely gravity-driven case, in which the fluid drains downwards and accumulates at the south pole, rotation leads to a migration of the maximum film thickness towards the equator, where the centrifugal force is the strongest.

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Han, Fengbo. "Cellular Automata Modeling of Ostwald Ripening and Rayleigh Instability." Materials 11, no. 10 (October 11, 2018): 1936. http://dx.doi.org/10.3390/ma11101936.

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A cellular automata (CA) approach to modeling both Ostwald ripening and Rayleigh instability was developed. Curvature-driven phase interface migration was implemented to CA model, and novel CA rules were introduced to ensure the conservation of phase volume fraction of nearly equilibrium two-phase system. For transient Ostwald ripening, it is shown that the temporal growth exponent m is evolving with time and non-integer temporal exponents between 2 and 3 are predicted. The varying temporal growth exponent m is related to the particle size distributions (PSDs) evolution. With an initial wide PSD, it becomes narrowed toward steady state. With an initial narrow PSD, it becomes widened at first and then narrowed toward steady state. For Rayleigh instability, two cases (one with sinusoidal perturbation on the surface of the long cylinder, and the other with grain boundaries in the interior of the long cylinder) were simulated, and the breakup of the long cylinder was shown for both cases. In the end, a system containing long cylinders with interior grain boundaries was simulated, which demonstrated the integration of Rayleigh instability and Ostwald ripening relating to the spheroidization of the lamellar structure.

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Droujinine, A., J. Pajchel, and K. Hitchen. "A study of sub-basalt depth imaging using the local Radon attributes on the Erlend Tertiary volcanic complex - North of Shetland, UK." Netherlands Journal of Geosciences - Geologie en Mijnbouw 87, no. 2 (August 2008): 135–49. http://dx.doi.org/10.1017/s0016774600023180.

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AbstractAcquiring conventional 3 km towed streamer data along a 2D profile in the North of Shetland (UK) enables us to use the local Radon-attributes within the context of depth processing methodology for accurate delineation of volcanic units and imaging beneath high-velocity layers. The objective is to map the radially-dipping structure of the Erlend pluton and to investigate the potential existence of relatively soft Cretaceous sediments underneath volcanic units. Success in the Erlend Volcano study requires strict attention to the separation between different groups of events. The crucial point is the generalized discrete Radon transform formulated in terms of local wavefront (dip and curvature) characteristics. This transform is utilized during pre-CMP processing and migration to minimize event-coupling artefacts. These artefacts represent cross-talk energy between various wave modes and include the unwanted part of the wavefield. We show how to produce detailed subsurface images within the region of interest (exploration prospect only) by applying the closely tied processes of prestack event enhancement and separation, well-driven time processing for velocity model building, and final event-based prestack depth imaging. Results show enhanced structural detail and good continuity of principal volcanic units and deeper reflections, suggesting a faulted 0.6 – 0.9 km thick layer of Cretaceous sediments in the proximity of well 209/09-1. Our interpretation complements existing low-resolution geophysical models inferred from gravity and wide-angle seismic data alone.

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Upmanyu, Moneesh, Zachary T. Trautt, and Branden B. Kappes. "Anisotropy in Grain Boundary Thermo-Kinetics: Atomic-Scale Computer Simulations." Materials Science Forum 467-470 (October 2004): 715–26. http://dx.doi.org/10.4028/www.scientific.net/msf.467-470.715.

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Anisotropy in grain boundary “thermo-kinetics” is central to our understanding of microstructural evolution during grain growth and recrystallization. This paper focusses on role of atomic-scale computer simulation techniques, in particular molecular dynamics (MD), in extracting fundamental grain boundary properties and elucidating the atomic-scale mechanisms that determine these properties. A brief overview of recent strides made in extraction of grain boundary mobility and energy is presented, with emphasis on plastic strain induced boundary motion (p-SIBM) during recrystallization and curvature driven boundary motion (CDBM) during grain growth. Simulations aimed at misorientation dependence of the grain boundary properties during p-SIBM and CDBM show that boundary mobility and energy exhibit extrema at high symmetry misorientations and boundary mobility is comparatively more anisotropic during CDBM. This suggests that boundary mobility is dependent on the driving force. Qualitative observations of the atomic-scale mechanisms in play during boundary motion corroborate the simulation data. p-SIBM is dominated by motion of dislocation-interaction induced stepped structure of the grain boundaries, while correlated shuffling of group of atoms preceded by rearrangement of grain boundary free volume due to single atomic-hops across the grain boundary is frequently observed during CDBM. Comparison of the simulation results with high-purity experimental data extracted in Al indicates that while there is excellent agreement in misorientation dependent anisotropic properties, there are significant differences in values of boundary mobility and migration activation enthalpy. This strongly suggests that minute concentration of impurities retard grain boundary kinetics via impurity drag. Finally, the paper briefly discusses current and future challenges facing the computer simulation community in studying grain boundary systems in real materials where extrinsic effects (vacancy, impurity, segregation and particle effects) significantly alter the microscopic structure-mechanism relations and play a decisive role in determining the boundary properties.

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Wei, Qiong, Xuechen Shi, Tiankai Zhao, Pingqiang Cai, Tianwu Chen, Yao Zhang, Changjin Huang, Jian Yang, Xiaodong Chen, and Sulin Zhang. "Actin-ring segment switching drives nonadhesive gap closure." Proceedings of the National Academy of Sciences 117, no. 52 (December 14, 2020): 33263–71. http://dx.doi.org/10.1073/pnas.2010960117.

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Gap closure to eliminate physical discontinuities and restore tissue integrity is a fundamental process in normal development and repair of damaged tissues and organs. Here, we demonstrate a nonadhesive gap closure model in which collective cell migration, large-scale actin-network fusion, and purse-string contraction orchestrate to restore the gap. Proliferative pressure drives migrating cells to attach onto the gap front at which a pluricellular actin ring is already assembled. An actin-ring segment switching process then occurs by fusion of actin fibers from the newly attached cells into the actin cable and defusion from the previously lined cells, thereby narrowing the gap. Such actin-cable segment switching occurs favorably at high curvature edges of the gap, yielding size-dependent gap closure. Cellular force microscopies evidence that a persistent rise in the radial component of inward traction force signifies successful actin-cable segment switching. A kinetic model that integrates cell proliferation, actin fiber fusion, and purse-string contraction is formulated to quantitatively account for the gap-closure dynamics. Our data reveal a previously unexplored mechanism in which cells exploit multifaceted strategies in a highly cooperative manner to close nonadhesive gaps.

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Chen, Tianchi, Andrew Callan-Jones, Eduard Fedorov, Andrea Ravasio, Agustí Brugués, Hui Ting Ong, Yusuke Toyama, et al. "Large-scale curvature sensing by directional actin flow drives cellular migration mode switching." Nature Physics 15, no. 4 (January 21, 2019): 393–402. http://dx.doi.org/10.1038/s41567-018-0383-6.

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Murray, A. Brad, and Andrew D. Ashton. "Instability and finite-amplitude self-organization of large-scale coastline shapes." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 371, no. 2004 (December 13, 2013): 20120363. http://dx.doi.org/10.1098/rsta.2012.0363.

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Recent research addresses the formation of patterns on sandy coastlines on alongshore scales that are large compared with the cross-shore extent of active sediment transport. A simple morphodynamic instability arises from the feedback between wave-driven alongshore sediment flux and coastline shape. Coastline segments with different orientations experience different alongshore sediment fluxes, so that curvatures in coastline shape drive gradients in sediment flux, which can augment the shoreline curvatures. In a simple numerical model, this instability, and subsequent finite-amplitude interactions between pattern elements, lead to a wide range of different rhythmic shapes and behaviours—ranging from symmetric cuspate capes and bays to alongshore migrating ‘flying spits’—depending on the characteristics of the input wave forcing. The scale of the pattern coarsens in some cases because of the merger of migrating coastline features, and in other cases because of non-local screening interactions between coastline protrusions, which affect the waves reaching other parts of the coastline. Features growing on opposite sides of an enclosed water body mutually affect the waves reaching each other in ways that lead to the segmentation of elongated water bodies. Initial tests of model predictions and comparison with observations suggest that modes of pattern formation in the model are relevant in nature.

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Liu, Iris B., Mohamed A. Gharbi, Victor L. Ngo, Randall D. Kamien, Shu Yang, and Kathleen J. Stebe. "Elastocapillary interactions on nematic films." Proceedings of the National Academy of Sciences 112, no. 20 (May 4, 2015): 6336–40. http://dx.doi.org/10.1073/pnas.1504817112.

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Rod-like colloids distort fluid interfaces and interact by capillarity. We explore this interaction at the free surface of aligned nematic liquid crystal films. Naive comparison of capillary and elastic energies suggests that particle assembly would be determined solely by surface tension. Here, we demonstrate that, under certain circumstances, the capillary and elastic effects are complementary and each plays an important role. Particles assemble end-to-end, as dictated by capillarity, and align along the easy axis of the director field, as dictated by elasticity. On curved fluid interfaces, however, curvature capillary energies can overcome the elastic orientations and drive particle migration along curvature gradients. Domains of dominant interaction and their transition are investigated.

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Rens, Elisabeth G., Mathé T. Zeegers, Iraes Rabbers, András Szabó, and Roeland M. H. Merks. "Autocrine inhibition of cell motility can drive epithelial branching morphogenesis in the absence of growth." Philosophical Transactions of the Royal Society B: Biological Sciences 375, no. 1807 (July 27, 2020): 20190386. http://dx.doi.org/10.1098/rstb.2019.0386.

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Epithelial branching morphogenesis drives the development of organs such as the lung, salivary gland, kidney and the mammary gland. It involves cell proliferation, cell differentiation and cell migration. An elaborate network of chemical and mechanical signals between the epithelium and the surrounding mesenchymal tissues regulates the formation and growth of branching organs. Surprisingly, when cultured in isolation from mesenchymal tissues, many epithelial tissues retain the ability to exhibit branching morphogenesis even in the absence of proliferation. In this work, we propose a simple, experimentally plausible mechanism that can drive branching morphogenesis in the absence of proliferation and cross-talk with the surrounding mesenchymal tissue. The assumptions of our mathematical model derive from in vitro observations of the behaviour of mammary epithelial cells. These data show that autocrine secretion of the growth factor TGF β 1 inhibits the formation of cell protrusions, leading to curvature-dependent inhibition of sprouting. Our hybrid cellular Potts and partial-differential equation model correctly reproduces the experimentally observed tissue-geometry-dependent determination of the sites of branching, and it suffices for the formation of self-avoiding branching structures in the absence and also in the presence of cell proliferation. This article is part of the theme issue ‘Multi-scale analysis and modelling of collective migration in biological systems’.

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Ielpi, Alessandro, and Mathieu G. A. Lapôtre. "Linking sediment flux to river migration in arid landscapes through mass balance." Journal of Sedimentary Research 92, no. 8 (August 22, 2022): 695–703. http://dx.doi.org/10.2110/jsr.2022.118.

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ABSTRACT Lateral migration is a key process shaping sinuous rivers and controlling sediment exchange with floodplains. The rate at which channels migrate is affected by bend curvature, bank erodibility, and sediment supply. The relationship between migration rate and sediment supply is poorly understood in dryland regions, where direct measurements are scarce. Here we propose a simple mass-balance model to estimate the sediment flux of ephemeral streams in North America's Great Basin and establish a comparison with timelapse photogrammetric data of lateral migration. The model takes into consideration variables such as long-term hillslope erosion, transient sediment storage in intra-catchment lowlands, and sediment bypass to depocenters. Our results point to first-order similarities in how sediment supply drives channel migration across diverse hydro-climatic regimes. However, we find that, for a given sediment supply and channel width, and despite their ephemeral discharge, dryland streams with minimal bank vegetation migrate about three times faster than humid-climate, vegetated ones. This difference in migration pace likely results from the compound effect of bank erodibility and bend geometry. Our model sheds new light on the driving mechanisms of channel mobility in dryland streams and may find application in assessing the sediment budgets of ungauged streams, reservoir trapping, and morphodynamic adjustments in stressed watersheds.

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Clubb, Fiona J., Simon M. Mudd, Martin D. Hurst, and Stuart W. D. Grieve. "Differences in channel and hillslope geometry record a migrating uplift wave at the Mendocino triple junction, California, USA." Geology 48, no. 2 (December 9, 2019): 184–88. http://dx.doi.org/10.1130/g46939.1.

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Abstract Tectonic plate motion, and the resulting change in land surface elevation, has been shown to have a fundamental impact on landscape morphology. Changes to uplift rates can drive a response in fluvial channels, which then drives changes to hillslopes. Because hillslopes respond on different time scales than fluvial channels, investigating the geometry of channels and hillslopes in concert provides novel opportunities to examine how uplift rates may have changed through time. Here we perform coupled topographic analysis of channel and hillslope geometry across a series of catchments at the Mendocino triple junction (MTJ) in northern California, USA. These catchments are characterized by an order-of-magnitude difference in uplift rate from north to south. We find that dimensionless hillslope relief closely matches the uplift signal across the area and is positively correlated with channel steepness. Furthermore, the range of uncertainty in hillslope relief is lower than that of channel steepness, suggesting that it may be a more reliable recorder of uplift in the MTJ region. We find that hilltop curvature lags behind relief in its response to uplift, which in turn lags behind channel response. These combined metrics show the northward migration of the MTJ and the corresponding uplift field from topographic data alone.

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ZOLEZZI, G., and G. SEMINARA. "Downstream and upstream influence in river meandering. Part 2. Planimetric development." Journal of Fluid Mechanics 438 (July 5, 2001): 183–211. http://dx.doi.org/10.1017/s002211200100427x.

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Perturbations of channel geometry (like variations of channel curvature or channel width) in meandering rivers give rise to morphodynamic effects which display themselves through the development of large-scale perturbations of bottom topography in the form of stationary bars developing in the longitudinal direction. The latter may then drive the lateral migration of the channel by enhancing bank erosion at bar pools: through this mechanism local perturbations of channel geometry may affect the planimetric development of meandering rivers on large timescales. The problem tackled herein is whether such morphodynamic influence is invariably felt downstream as the commonly employed model of river meandering would suggest.In order to solve this problem, we derive the exact solution of the linearized form of the mathematical problem of river morphodynamics. Linear analysis had pointed out the existence of a resonance phenomenon: in a linear (hence ideal) context, resonance occurs when the meander wavenumber and the width ratio of the channel take values (λR and βR, respectively) such as to force free spatial modes of the system consisting of free bars which neither grow nor decay either in time or in space. Channels characterized by values of the width ratio β larger (smaller) than βR are called super- (sub-)resonant. The present solution, which applies to channels with constant width and arbitrary curvature distribution, shows that two distinct scenarios may occur: downstream influence is associated with sub-resonant channels and vice versa dominant upstream influence occurs in super-resonant channels. Small-amplitude waves of bottom topography are shown to migrate downstream in the former case and may migrate upstream in the latter, as resonance also defines the threshold conditions below (above) which small-amplitude alternate bar perturbations (may) migrate downstream (upstream).These results have several implications. In the present paper we examine the overdeepening phenomenon whereby abrupt variations of channel curvature, as in sequences of straight and constant curvature reaches, lead to sequences of stationary alternate bars with amplitude decaying in the longitudinal direction. We show that, along with downstream overdeepening, an upstream overdeepening scenario is predicted in the super-resonant regime.Implications of the upstream influence on planimetric development of meandering rivers are investigated in Part 2.

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Fernández, Roberto, Gary Parker, and Colin P. Stark. "Experiments on patterns of alluvial cover and bedrock erosion in a meandering channel." Earth Surface Dynamics 7, no. 4 (October 9, 2019): 949–68. http://dx.doi.org/10.5194/esurf-7-949-2019.

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Abstract. In bedrock rivers, erosion by abrasion is driven by sediment particles that strike bare bedrock while traveling downstream with the flow. If the sediment particles settle and form an alluvial cover, this mode of erosion is impeded by the protection offered by the grains themselves. Channel erosion by abrasion is therefore related to the amount and pattern of alluvial cover; these are functions of sediment load and hydraulic conditions, which in turn are functions of channel geometry, slope, and sinuosity. This study presents the results of alluvial cover experiments conducted in a meandering channel flume of high fixed sinuosity. Maps of quasi-instantaneous alluvial cover were generated from time-lapse imaging of flows under a range of below-capacity bedload conditions. These maps were used to infer patterns of particle impact frequency and likely abrasion rates. Results from eight such experiments suggest the following: (i) abrasion through sediment particle impacts is driven by fluctuations in alluvial cover due to the movement of freely migrating bars; (ii) patterns of potential erosion are functions of sediment load and local curvature; (iii) low sediment supply ratios are associated with regions of potential erosion located closer to the inner bank, but this region moves toward the outer bank as sediment supply increases; and (iv) the threads of high erosion rates are located at the toe of the alluvial bars, just where the alluvial cover reaches an optimum for abrasion.

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Dikpati, Mausumi, Aimee A. Norton, Scott W. McIntosh, and Peter A. Gilman. "Dynamical Splitting of Spot-producing Magnetic Rings in a Nonlinear Shallow-water Model." Astrophysical Journal 922, no. 1 (November 1, 2021): 46. http://dx.doi.org/10.3847/1538-4357/ac1359.

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Abstract We explore the fundamental physics of narrow toroidal rings during their nonlinear magnetohydrodynamic evolution at tachocline depths. Using a shallow-water model, we simulate the nonlinear evolution of spot-producing toroidal rings of 6° latitudinal width and a peak field of 15 kG. We find that the rings split; the split time depends on the latitude of each ring. Ring splitting occurs fastest, within a few weeks, at latitudes 20°–25°. Rossby waves work as perturbations to drive the instability of spot-producing toroidal rings; the ring split is caused by the “mixed stress” or cross-correlations of perturbation velocities and magnetic fields, which carry magnetic energy and flux from the ring peak to its shoulders, leading to the ring split. The two split rings migrate away from each other, the high-latitude counterpart slipping poleward faster due to migrating mixed stress and magnetic curvature stress. Broader toroidal bands do not split. Much stronger rings, despite being narrow, do not split due to rigidity from stronger magnetic fields within the ring. Magnetogram analysis indicates the emergence of active regions sometimes at the same longitudes but separated in latitude by 20° or more, which could be evidence of active regions emerging from split rings, which consistently contribute to observed high-latitude excursions of butterfly wings during the ascending, peak, and descending phases of a solar cycle. Observational studies in the future can determine how often new spots are found at higher latitudes than their lower-latitude counterparts and how the combinations influence solar eruptions and space weather events.

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Finotello, Alvise, Alessandro Ielpi, Mathieu G. A. Lapôtre, Eli D. Lazarus, Massimiliano Ghinassi, Luca Carniello, Serena Favaro, Davide Tognin, and Andrea D’Alpaos. "Vegetation enhances curvature-driven dynamics in meandering rivers." Nature Communications 15, no. 1 (March 4, 2024). http://dx.doi.org/10.1038/s41467-024-46292-x.

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AbstractStabilization of riverbanks by vegetation has long been considered necessary to sustain single-thread meandering rivers. However, observation of active meandering in modern barren landscapes challenges this assumption. Here, we investigate a globally distributed set of modern meandering rivers with varying riparian vegetation densities, using satellite imagery and statistical analyses of meander-form descriptors and migration rates. We show that vegetation enhances the coefficient of proportionality between channel curvature and migration rates at low curvatures, and that this effect wanes in curvier channels irrespective of vegetation density. By stabilizing low-curvature reaches and allowing meanders to gain sinuosity as channels migrate laterally, vegetation quantifiably affects river morphodynamics. Any causality between denser vegetation and higher meander sinuosity, however, cannot be inferred owing to more frequent avulsions in modern non-vegetated environments. By illustrating how vegetation affects channel mobility and floodplain reworking, our findings have implications for assessing carbon stocks and fluxes in river floodplains.

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Frost, H. J., Y. Hayashi, C. V. Thompson, and D. T. Walton. "The Effect of Solute Drag on Grain Growth in Thin Films." MRS Proceedings 317 (1993). http://dx.doi.org/10.1557/proc-317-431.

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ABSTRACTWe have modelled the microstructural evolution of polycrystalline thin films during grain growth under the situation in which grain boundary migration becomes impeded by solute drag. For this we use a two-dimensional simulation of capillarity-driven grain growth in which grain boundaries migrate at velocities proportional to local curvature. At high driving forces, corresponding to high curvatures, the boundaries are given a mobility corresponding to drag-free motion. At low driving forces, corresponding to curvatures less than some critical value, the boundaries are given a lower mobility which models the effect of solute drag. During grain growth the average curvature of boundary segments decreases. When the boundary curvatures begin to fall below the critical curvature, the grain size distribution evolves to a lognormal distribution, which is maintained as significant further grain growth occurs. This is in accordance with many experimental grain size distributions which are commonly observed to be lognormal.

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Ghigliotti, Giovanni, Abtin Rahimian, George Biros, and Chaouqi Misbah. "Vesicle Migration and Spatial Organization Driven by Flow Line Curvature." Physical Review Letters 106, no. 2 (January 10, 2011). http://dx.doi.org/10.1103/physrevlett.106.028101.

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38

Sadhu, Raj Kumar, Marine Luciano, Wang Xi, Cristina Martinez-Torres, Marcel Schröder, Christoph Blum, Marco Tarantola, et al. "A minimal physical model for curvotaxis driven by curved protein complexes at the cell’s leading edge." Proceedings of the National Academy of Sciences 121, no. 12 (March 15, 2024). http://dx.doi.org/10.1073/pnas.2306818121.

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Cells often migrate on curved surfaces inside the body, such as curved tissues, blood vessels, or highly curved protrusions of other cells. Recent in vitro experiments provide clear evidence that motile cells are affected by the curvature of the substrate on which they migrate, preferring certain curvatures to others, termed “curvotaxis.” The origin and underlying mechanism that gives rise to this curvature sensitivity are not well understood. Here, we employ a “minimal cell” model which is composed of a vesicle that contains curved membrane protein complexes, that exert protrusive forces on the membrane (representing the pressure due to actin polymerization). This minimal-cell model gives rise to spontaneous emergence of a motile phenotype, driven by a lamellipodia-like leading edge. By systematically screening the behavior of this model on different types of curved substrates (sinusoidal, cylinder, and tube), we show that minimal ingredients and energy terms capture the experimental data. The model recovers the observed migration on the sinusoidal substrate, where cells move along the grooves (minima), while avoiding motion along the ridges. In addition, the model predicts the tendency of cells to migrate circumferentially on convex substrates and axially on concave ones. Both of these predictions are verified experimentally, on several cell types. Altogether, our results identify the minimization of membrane-substrate adhesion energy and binding energy between the membrane protein complexes as key players of curvotaxis in cell migration.

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Trautt, Z., and M. Upmanyu. "Atomic-Scale Simulation of Grain Boundary Kinetics during Recrystallization." MRS Proceedings 819 (2004). http://dx.doi.org/10.1557/proc-819-n6.7.

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AbstractWe present two-dimensional molecular dynamics (MD) simulations of symmetric tilt grain boundary kinetics, driven by stored energy of deformation. The latter is introduced by prescribing a well-defined gradient in dislocation density across a flat grain boundary. Bicrystals simulations reveal that the boundary motion, albeit jerky, increases linearly with simulation time. We also employ a control simulation to extract the driving force for motion, which then yields a unique boundary mobility. Preliminary comparisons with curvature driven boundary migration for misorientations 30° and 22.78° suggest that misorientation dependence of boundary migration is significantly less anisotropic, in turn implying that the mechanism of motion itself is different.

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Merkle, K. L., L. J. Thompson, and F. Phillipp. "Dynamics of grain boundary motion at the atomic level." MRS Proceedings 819 (2004). http://dx.doi.org/10.1557/proc-819-n6.1.

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AbstractGrain boundaries (GBs) in polycrystalline materials play a pivotal role in controlling their mechanical and physical behavior. High-resolution electron microscopy (HREM) was used to study thermally activated GB migration in thin films of Al and Au at elevated temperatures (T > 0.5 Tm). Grain boundary engineering via epitaxial templating allowed the manufacture of well-defined grain and interfacial geometries. These techniques enabled the observation of tilt, but also twist and general GBs at atomic resolution in-situ at high temperatures. Surface-energy driven GB migration occurred in general GBs, whereas tilt GB motion was curvature driven. Digital analysis of HREM video recordings have given considerable insight in the dynamics of GB motion at elevated temperatures. It is not surprising that the complex and diverse migration mechanisms depend on GB geometry as well as on interatomic interactions. The results provide, among others, direct evidence for collective effects by concerted atomic shuffles, ledge propagation in (113) symmetric tilt GBs, and motions of triple junctions at elevated temperatures.

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Li, Y., and A. B. Limaye. "Timescale of the Morphodynamic Feedback Between Planform Geometry and Lateral Migration of Meandering Rivers." Journal of Geophysical Research: Earth Surface 129, no. 2 (February 2024). http://dx.doi.org/10.1029/2023jf007413.

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AbstractAcross varied environments, meandering channels evolve through a common morphodynamic feedback: the sinuous channel shape causes spatial variations in boundary shear stress, which cause lateral migration rates to vary along a meander bend and change the shape of the channel. This feedback is embedded in all conceptual models of meandering channel migration, and in numerical models, it occurs over an explicit timescale (i.e., the model time step). However, the sensitivity of modeled channel trajectory to the time step is unknown. In numerical experiments using a curvature‐driven model of channel migration, we find that channel trajectories are consistent over time if the channel migrates ≤10% of the channel width over the feedback timescale. In contrast, channel trajectories diverge if the time step causes migration to exceed this threshold, due to the instability in the co‐evolution of channel curvature and migration rate. The divergence of channel trajectories accumulates with the total run time. Application to hindcasting of channel migration for 10 natural rivers from the continental US and the Amazon River basin shows that the sensitivity of modeled channel trajectories to the time step is greatest at low (near‐unity) channel sinuosity. A time step exceeding the criterion causes over‐prediction of the width of the channel belt developed over millennial timescales. These findings establish a geometric constraint for predicting channel migration in landscape evolution models for lowland alluvial rivers, upland channels coupled to hillslopes and submarine channels shaped by turbidity currents, over timescales from years to millennia.

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Ishii, Mamoru, Tomoko Tateya, Michiyuki Matsuda, and Tsuyoshi Hirashima. "Stalling interkinetic nuclear migration in curved pseudostratified epithelium of developing cochlea." Royal Society Open Science 8, no. 12 (December 2021). http://dx.doi.org/10.1098/rsos.211024.

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The bending of epithelial tubes is a fundamental process in organ morphogenesis, driven by various multicellular behaviours. The cochlea in the mammalian inner ear is a representative example of spiral tissue architecture where the continuous bending of the duct is a fundamental component of its morphogenetic process. Although the cochlear duct morphogenesis has been studied by genetic approaches extensively, it is still unclear how the cochlear duct morphology is physically formed. Here, we report that nuclear behaviour changes are associated with the curvature of the pseudostratified epithelium during murine cochlear development. Two-photon live-cell imaging reveals that the nuclei shuttle between the luminal and basal edges of the cell is in phase with cell-cycle progression, known as interkinetic nuclear migration, in the flat region of the pseudostratified epithelium. However, the nuclei become stationary on the luminal side following mitosis in the curved region. Mathematical modelling together with perturbation experiments shows that this nuclear stalling facilitates luminal-basal differential growth within the epithelium, suggesting that the nuclear stalling would contribute to the bending of the pseudostratified epithelium during the cochlear duct development. The findings suggest a possible scenario of differential growth which sculpts the tissue shape, driven by collective nuclear dynamics.

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Zhang, Z. Y., X. K. Meng, J. Wang, Hanchen Huang, and X. Y. Liu. "Growth study of nanocrystalline Ni and Ni3Al using molecular dynamics." MRS Proceedings 978 (2006). http://dx.doi.org/10.1557/proc-978-0978-gg13-09.

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AbstractThe growth of nanocrystalline materials has received much attention recently due to its importance in nanocrystalline thin film properties and fabrications. Research studies of this subject have so far focused on the face-centered-cubic metals. Two mechanisms, grain-rotation induced grain coalescence and curvature-driven grain-boundary migration are considered as the dominant mechanisms in the nanograin growth. In this work, we use molecular dynamics method to simulate the growth of Ni and Ni3Al alloy. We find the above mechanisms can describe the growth behavior well. A detailed comparison of the nanograin growth between the two systems is discussed in terms of grain rotation and grain sliding. We also study the temperature effect and the size effect in the nanograin growth. The tendency of twinning in the nanograin growth is discussed.

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Dorsey, Rebecca J., Sergio G. Longhitano, and Domenico Chiarella. "Structure and morphology of an active conjugate relay zone, Messina Strait, southern Italy." Basin Research, August 25, 2023. http://dx.doi.org/10.1111/bre.12818.

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AbstractMessina Strait is a narrow fault‐bounded marine basin that separates the Calabrian peninsula from Sicily in southern Italy. It sits in a seismically active region where normal fault scarps and raised Quaternary marine terraces record ongoing extension driven by southeastward rollback of the Calabrian subduction zone. A review of published studies and new data shows that normal faults in the Messina Strait region define a conjugate relay zone where displacement is transferred along strike from NW‐dipping normal faults in the northeast (southern Calabria) to the SE‐dipping Messina‐Taormina normal fault in the southwest (offshore eastern Sicily). The narrow marine strait is a graben undergoing active subsidence within the relay zone, where pronounced curvature of normal faults results from large strain gradients and clockwise rotations related to fault interactions. Based on regional fault geometries and published age constraints, we infer that normal faults in southern Calabria migrated northwest while normal faults in NE Sicily migrated southeast during the past ca. 2–2.5 Myr. This pattern has resulted in tectonic narrowing of the strait through time by inward migration of facing normal faults and rapid mantle‐driven uplift.

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45

Ming, Wenjie, Boyuan Huang, Sizheng Zheng, Yinxin Bai, Junling Wang, Jie Wang, and Jiangyu Li. "Flexoelectric engineering of van der Waals ferroelectric CuInP ₂ S ₆." Science Advances 8, no. 33 (August 19, 2022). http://dx.doi.org/10.1126/sciadv.abq1232.

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Van der Waals layered CuInP 2 S 6 (CIPS) is an ideal candidate for developing two-dimensional microelectronic heterostructures because of its room temperature ferroelectricity, although field-driven polarization reversal of CIPS is intimately coupled with ionic migration, often causing erratic and damaging switching that is highly undesirable for device applications. In this work, we develop an alternative switching mechanism for CIPS using flexoelectric effect, abandoning external electric fields altogether, and the method is motivated by strong correlation between polarization and topography variation of CIPS. Phase-field simulation identifies a critical radius of curvature around 5 μm for strain gradient to be effective, which is realized by engineered topographic surfaces using silver nanowires and optic grating upon which CIPS is transferred to. We also demonstrate mechanical modulation of CIPS on demand via strain gradient underneath a scanning probe, making it possible to engineer multiple polarization states of CIPS for device applications.

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46

Slater, Brandon, Wonyeong Jung, and Taeyoon Kim. "Emergence of diverse patterns driven by molecular motors in the motility assay." Cytoskeleton, November 10, 2023. http://dx.doi.org/10.1002/cm.21808.

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AbstractActomyosin contractility originating from interactions between F‐actin and myosin motors in the actin cytoskeleton generates mechanical forces and drives a wide range of cellular processes including cell migration and cytokinesis. To probe the interactions between F‐actin and myosin motors, the myosin motility assay has been popularly employed, which consists of myosin heads attached to a glass surface and F‐actins gliding on the surface via interactions with the heads. Several experiments have shown that F‐actins move in a collective fashion due to volume‐exclusion effects between neighboring F‐actins. Furthermore, Computational models have shown how changes in key parameters lead to diverse pattern formation in motility assay. However, in most of the computational models, myosin motors were implicitly considered by applying a constant propulsion force to filaments to reduce computational cost. This simplification limits the physiological relevance of the insights provided by the models and potentially leads to artifacts. In this study, we employed an agent‐based computational model for the motility assay with explicit immobile motors interacting with filaments. We rigorously account for the kinetics of myosin motors including the force‐velocity relationship for walking and the binding and unbinding behaviors. We probed the effects of the length, rigidity, and concentration of filaments and repulsive strength on collective movements and pattern formation. It was found that four distinct types of structures—homogeneous networks, flocks, bands, and rings—emerged as a result of collisions between gliding filaments. We further analyzed the frequency and morphology of these structures and the curvature, alignment, and rotational motions of filaments. Our study provides better insights into the origin and properties of patterns formed by gliding filaments beyond what was shown before.

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47

Maekawa, Masashi, Ren Natsume, and Makoto Arita. "Functional significance of ion channels during macropinosome resolution in immune cells." Frontiers in Physiology 13 (October 20, 2022). http://dx.doi.org/10.3389/fphys.2022.1037758.

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Macropinocytosis is a unique type of endocytosis accompanied by membrane ruffle formation. Closure of membrane ruffles leads to the uptake of large volumes of fluid phase and, subsequently, the formation of large vacuoles termed macropinosomes. Immune cells, such as dendritic cells, T cells, and macrophages, endocytose the surrounding amino acids and pathogens via macropinocytosis either constitutively or in a stimulus-dependent fashion. This process is critical for cell migration, mammalian target of rapamycin complex 1 (mTORC1) activation, and antigen presentation. Large vacuoles are fragmented into tubules and smaller vesicles during the progression and maturation of macropinosomes in immune cells. This process is called “macropinosome resolution” and requires osmotically driven shrinkage of macropinosomes, which is controlled by ion channels present in them. The crenation of membranes on shrunken macropinosomes is recognized by curvature-sensing proteins and results in intracellular membrane trafficking. In this mini review, we highlight the recent progress in research on macropinosome resolution in macrophages, with a focus on ion channels (TPC1/2 for Na+ and TMEM206 for Cl−) that is required for macropinosome resolution. We also discuss the potential contribution of membrane lipids to this process.

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Weiss, Samantha F., and Jonathan J. L. Higdon. "Dynamics of meandering rivers in finite-length channels: linear theory." Journal of Fluid Mechanics 938 (March 17, 2022). http://dx.doi.org/10.1017/jfm.2022.131.

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Meandering channels are dynamic landforms that arise as a result of fluid mechanic and sedimentary processes. Their evolution has been described by the meander-morphodynamic equations, which dictate that channel curvature and bed topography give rise to local perturbations in streamwise fluid velocity, prompting the preferential erosion and sediment deposition that constitute meander behaviour. Novel mathematical conditions are presented to guarantee unique solutions for the linearized equations in non-periodic domains with finite boundaries. With the boundary condition specification sufficient for the uniqueness proof one finds a well-posed initial-boundary-value problem amenable to standard numerical techniques for partial differential equations. This provides a pathway for improved numerical algorithms for simulations of meandering river dynamics. Previous theoretical analysis for linear stability theory in meandering dynamics has been restricted to spatially periodic systems. The present effort develops new results for linear stability theory in non-periodic systems with temporal driving at system boundaries as well as non-homogeneous initial conditions. Predictions for temporal driving at the inlets for non-periodic finite domains provide clarification for observed behaviour in laboratory flumes where driven conditions at the inlet avoids the long-term decay of all meanders observed in flumes with fixed entry conditions. Linear stability theory for finite domains confirms that a continuous perturbation is required for sustained meandering. Original scaling arguments are presented for the dependence of the meander migration rate on geological parameters, showing that the rate of channel migration increases with increased width, downreach slope and bank erodibility, and decreases with increased volumetric flow rate.

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Xu, Hongmei, Yucheng Huo, Quan Zhou, Lianghao Abraham Wang, Pingqiang Cai, Bryant Doss, Changjin Huang, and K. Jimmy Hsia. "Geometry-mediated bridging drives nonadhesive stripe wound healing." Proceedings of the National Academy of Sciences 120, no. 18 (April 25, 2023). http://dx.doi.org/10.1073/pnas.2221040120.

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Wound healing through reepithelialization of gaps is of profound importance to the medical community. One critical mechanism identified by researchers for closing non-cell-adhesive gaps is the accumulation of actin cables around concave edges and the resulting purse-string constriction. However, the studies to date have not separated the gap-edge curvature effect from the gap size effect. Here, we fabricate micropatterned hydrogel substrates with long, straight, and wavy non-cell-adhesive stripes of different gap widths to investigate the stripe edge curvature and stripe width effects on the reepithelialization of Madin–Darby canine kidney (MDCK) cells. Our results show that MDCK cell reepithelization is closely regulated by the gap geometry and may occur through different pathways. In addition to purse-string contraction, we identify gap bridging either via cell protrusion or by lamellipodium extension as critical cellular and molecular mechanisms for wavy gap closure. Cell migration in the direction perpendicular to wound front, sufficiently small gap size to allow bridging, and sufficiently high negative curvature at cell bridges for actin cable constriction are necessary/sufficient conditions for gap closure. Our experiments demonstrate that straight stripes rarely induce cell migration perpendicular to wound front, but wavy stripes do; cell protrusion and lamellipodia extension can help establish bridges over gaps of about five times the cell size, but not significantly beyond. Such discoveries deepen our understanding of mechanobiology of cell responses to curvature and help guide development of biophysical strategies for tissue repair, plastic surgery, and better wound management.

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Addula, Ravi Kumar Reddy, and Baron Peters. "Kinetic coefficient for ice-water interface from simulated non-equilibrium relaxation at coexistence." Journal of Chemical Physics, October 14, 2022. http://dx.doi.org/10.1063/5.0124848.

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In the theory of solidification, the kinetic coefficient multiplies the local supercooling to give the solid-liquid interface velocity. The same coefficient should drive interface migration at the coexistence temperature in proportion to a curvature force. This work computes the ice-water kinetic coefficient from molecular simulations starting from a sinusoidal ice-water interface at the coexistence temperature. We apply this method to the basal and prismatic ice planes and compare results to previous estimates from equilibriumcorrelation functions and simulations at controlled supercooling.

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Journal articles on the topic 'Curvature driven migration'

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