Formation Of Multiple Rings Research Articles

Habitat generalist species constrain the diversity of mimicry rings in heterogeneous habitats

How evolution creates and maintains trait patterns in species-rich communities is still an unsolved topic in evolutionary ecology. One classical example of community-level pattern is the unexpected coexistence of different mimicry rings, each of which is a group of mimetic species with the same warning signal. The coexistence of different mimicry rings in a community seems paradoxical because selection among unpalatable species should favor convergence to a single warning pattern. We combined mathematical modeling based on network theory and numerical simulations to explore how different types of selection, such as mimetic and environmental selections, and habitat use by mimetic species influence the formation of coexisting rings. We show that when habitat and mimicry are strong sources of selection, the formation of multiple rings takes longer due to conflicting selective pressures. Moreover, habitat generalist species decrease the distinctiveness of different mimicry rings’ patterns and a few habitat generalist species can generate a “small-world effect”, preventing the formation of multiple mimicry rings. These results may explain why the coexistence of mimicry rings is more common in groups of animals that tend towards habitat specialism, such as butterflies.

Morphogenesis and characterization of wheat xerogel structure and insights into its 4D transformation

• The wheat polymers undergo concentration, deformation, and coalescence during drying. • The solid fraction increases as the horizontal and vertical drying front proceeds. • Characterization of wheat xerogel reveals dense top and porous bottom surfaces. • The wheat xerogel exhibits shape transition in hot water by anisotropic swelling. The pioneering concept in additive manufacturing is the four-dimensional (4D) materials. The material science approach is required to design the complex stimuli-responsive food structures. Wheat flour components were engineered by gelatinizing and drying as a macroscopic sessile droplet. The morphogenesis of gelatinized wheat flour suspension into hydrogel and xerogel through evaporation-driven self-assembly mechanism follows concentration, deformation, and coalescence similar to the film formation process throughout the drying time. The characterization of the top surface of xerogel showed continuous smooth topography while bottom revealed a porous surface with multiple ring formation. During the xerogel development, there is no change in the chemical nature of wheat flour. When immersed in water, xerogel swells variably in different directions due to its heterogeneous particle arrangement. Anisotropic swelling creates a stress gradient in the xerogel, causing a self-bending mechanism. This research provides insights to the next generation cutting edge food processing technique, 4D foods (i.e.) foods with the ability to change shape from flat thin food material to programmed 3D shapes before consumption. In food research, this concept can initiate the development of food products with unique feature of shape-shifting.

Revised Description of Dust Diffusion and a New Instability Creating Multiple Rings in Protoplanetary Disks

Abstract Various instabilities have been proposed as a promising mechanism for accumulating dust. Moreover, some of them are expected to lead to multiple-ring structure formation and planetesimal formation in protoplanetary disks. In a turbulent gaseous disk, the growth of the instabilities and the dust accumulation are quenched by the turbulent diffusion of dust grains. The diffusion process has often been modeled by a diffusion term in the continuity equation for the dust density. The dust diffusion model, however, does not guarantee conservation of angular momentum in a disk. In this study, we first formulate equations that describe dust diffusion and also conserve the total angular momentum of a disk. Second, we perform a linear perturbation analysis on the secular gravitational instability (GI) using the equations. The results show that the secular GI is a monotonically growing mode, contrary to the result of previous analyses that found it overstable. We find that the overstability is caused by the nonconservation of the angular momentum. Third, we find a new axisymmetric instability due to the combination of dust–gas friction and turbulent gas viscosity, which we refer to as two-component viscous gravitational instability (TVGI). The most unstable wavelength of TVGI is comparable to or smaller than the gas scale height. TVGI accumulates dust grains efficiently, which indicates that TVGI is a promising mechanism for the formation of multiple-ring-like structures and planetesimals. Finally, we examine the validity of the ring formation via the secular GI and TVGI in the HL Tau disk and find both instabilities can create multiple rings whose width is about 10 au at orbital radii larger than 50 au.

Multiple Spiral Arms in Protoplanetary Disks: Linear Theory

Abstract Recent observations of protoplanetary disks, as well as simulations of planet–disk interaction, have suggested that a single planet may excite multiple spiral arms in the disk, in contrast to the previous expectations based on linear theory (predicting a one-armed density wave). We reassess the origin of multiple arms in the framework of linear theory by solving for the global two-dimensional response of a nonbarotropic disk to an orbiting planet. We show that the formation of a secondary arm in the inner disk, at about half of the orbital radius of the planet, is a robust prediction of linear theory. This arm becomes stronger than the primary spiral at several tenths of the orbital radius of the planet. Several additional, weaker spiral arms may also form in the inner disk. On the contrary, a secondary spiral arm is unlikely to form in the outer disk. Our linear calculations, fully accounting for the global behavior of both the phases and amplitudes of perturbations, generally support the recently proposed WKB phase argument for the secondary arm origin (as caused by the intricacy of constructive interference of the azimuthal harmonics of the perturbation at different radii). We provide analytical arguments showing that the process of a single spiral wake splitting up into multiple arms is a generic linear outcome of wave propagation in differentially rotating disks. It is not unique to planet-driven waves and also occurs in linear calculations of spiral wakes freely propagating with no external torques. These results are relevant for understanding formation of multiple rings and gaps in protoplanetary disks.

Macroscopic Dynamics of Dust Grains and Formation of Multiple Rings in Protoplanetary Disks

Macroscopic Dynamics of Dust Grains and Formation of Multiple Rings in Protoplanetary Disks

Non-linear development of secular gravitational instability in protoplanetary disks

Abstract We perform non-linear simulation of secular gravitational instability (GI) in protoplanetary disks, which has been proposed as a mechanism of planetesimal and multiple ring formation. Since the timescale of the growth of the secular GI is much longer than the Keplerian rotation period, we develop a new numerical scheme for a long-term calculation utilizing the concept of symplectic integration. With our new scheme, we first investigate the non-linear development of the secular GI in a disk without a pressure gradient in the initial state. We find that the surface density of dust increases by more than a factor of 100 while that of gas does not increase even by a factor of 2, which results in the formation of dust-dominated rings. A line mass of the dust ring tends to be very close to the critical line mass of a self-gravitating isothermal filament. Our results indicate that the non-linear growth of the secular GI provides a powerful mechanism to concentrate the dust. We also find that the dust ring formed via the non-linear growth of the secular GI migrates inward with a low velocity, which is driven by the self-gravity of the ring. We give a semi-analytical expression for the inward migration speed of the dusty ring.

Direct observation of nanoparticle multiple-ring pattern formation during droplet evaporation with dark-field microscopy.

Controllable protocols towards nanoparticle self-assembly are important for applications of functional nanomaterials. Evaporation is a simple yet effective method to realize a gold nanoparticle ordered self-assembly, but until now, little attention has been paid to viewing the corresponding assembly process. Herein, with the help of dark-field microscopy, we in situ monitored the whole dynamic process of gold nanorod (GNR) assembly as the solvent evaporated. Differently from the previous coffee-ring effect, rod-shaped hydrophilic GNRs, within certain concentrations, spontaneously assembled into a multiple-ring pattern on a hydrophobic substrate via droplet drying. The self-assembly mechanism is consistent with a diffusion-driven kinetics, and the influencing factors, including the GNR surface modification, the colloid concentration, the surface property of the substrate, and the shape of the nanoparticles, were systematically investigated.

Generating a three-dimensional dark focus from a single conically refracted light beam

We report here the generation of a three-dimensional (3D) dark focus from a single focused monochromatic Gaussian beam that undergoes conical refraction when it propagates along one of the optic axes of a biaxial crystal. We study the resulting ring intensity pattern behind the crystal as a function of the ratio between the ring radius and the beam waist and derive the particular parameter values for which a 3D dark focus with null intensity at the ring center is formed. We have performed experiments with a KGd(WO(4))(2) biaxial crystal, reporting the generation of a bottle beam in full agreement with our theoretical investigations.

Pattern formation in the exciton inner ring

We report on the spatially separated pump-probe study of indirect excitons in the inner ring in the exciton emission pattern. A pump laser beam generates the inner ring and a weaker probe laser beam is positioned in the inner ring. The probe beam is found to suppress the exciton emission intensity in the ring. We also report on the inner ring fragmentation and formation of multiple rings in the inner ring region. These features are found to originate from a weak spatial modulation of the excitation beam intensity in the inner ring region. The modulation of exciton emission intensity anti-correlates with the modulation of the laser excitation intensity. The three phenomena - inner ring fragmentation, formation of multiple rings in the inner ring region, and emission suppression by a weak probe laser beam - have a common feature: a reduction of exciton emission intensity in the region of enhanced laser excitation. This effect is explained in terms of exciton transport and thermalization.

Multiple rings formation in cascaded conical refraction

When a light beam passes through a cascade of biaxial crystals (BCs) with aligned optic axes, the resulting transverse intensity pattern consists of multiple concentric rings. We provide a simple formulation for the pattern formation for both circularly and linearly polarized input beams, that could be applied for a cascade of an arbitrary number of BCs. We have experimentally investigated multiple ring formation with up to three cascade BCs, showing that the theoretical formulation is in full agreement with the experimental results.

Mathematical model for positioning the FtsZ contractile ring in Escherichia coli

During bacterial cytokinesis, a proteinaceous contractile ring assembles in the cell middle. The Z ring tethers to the membrane and contracts, when triggered, to form two identical daughter cells. One mechanism for positioning the ring involves the MinC, MinD and MinE proteins, which oscillate between cell poles to inhibit ring assembly. Averaged over time, the concentration of the inhibitor MinC is lowest at midcell, restricting ring assembly to this region. A second positioning mechanism, called Nucleoid Occlusion, acts through protein SlmA to inhibit ring polymerization in the location of the nucleoid. Here, a mathematical model was developed to explore the interactions between Min oscillations, nucleoid occlusion, Z ring assembly and positioning. One-dimensional advection-reaction-diffusion equations were built to simulate the spatio-temporal concentrations of Min proteins and their effect on various forms of FtsZ. The resulting partial differential equations were numerically solved using a finite volume method. The reduced chemical model assumed that the ring is composed of overlapping FtsZ filaments and that MinC disrupts lateral interactions between filaments. SlmA was presumed to break long FtsZ filaments into shorter units. A term was developed to account for the movement of FtsZ subunits in membrane-bound filaments as they touch and align with other filaments. This alignment was critical in forming sharp stable rings. Simulations qualitatively reproduced experimental results showing the incorrect positioning of rings when Min proteins were not expressed, and the formation of multiple rings when FtsZ was overexpressed.

Numerical investigation on mechanism of multiple vortex rings formation in late boundary-layer transition

Mechanism of multiple vortex ring formation is one of key issues of late flow transition in a boundary layer. In this paper, a new mechanism is presented that the multiple ring formation is a result of shear layer instability. According to our DNS observation, a momentum deficit zone is formed above the original hairpin vortex tube due to the ejection of the streamwise hairpin vortex tube, which brings the low speed flow from the lower level to the higher level of the boundary layer through vortex rotation. Then the momentum deficit zone generates a sharp olive-shaped shear layer surrounded by the high speed flow. As the shear layer moves up, inviscid instability is developed due to the existence of inflection points (inflection surface in 3-D). Consequently, the new vortex rings are formed one by one. During the new spanwise vortex ring formation process, the spanwise vorticity is increased; however, the original streamwise hairpin vortex tube is weakened with decreasing of the streamwise vorticity. This process follows the Helmoholtz vorticity conservation law.

Fast fused rings

A phosphine catalyses the formation of multiple rings and stereocentres in a single step from a simple linear precursor.

Evaporative Self-Assembly from Complex DNA−Colloid Suspensions

Evaporation-induced pattern formation has attracted considerable attention as a simple yet versatile method for generating self-assembled structures that have broad applications from photonic devices to biomacromolecular recognition. Previous study of evaporative self-assembly has mainly focused on single nonvolatile component systems, and the driving mechanisms have been extensively investigated. In contrast, pattern formation from evaporating multicomponent systems, despite its wide existence in nature and numerous engineering applications, has been rarely explored. In this work, we examine a DNA-colloid binary suspension as a model system to understand the evaporation-induced interfacial hydrodynamics and self-assembled morphology in multicomponent systems involving complex competing intermolecular and interfacial interactions. Direct microscopic observations show that the composition of the binary system plays a critical role in the multiple-ring formation upon evaporation: (1) suspensions with high DNA concentrations and low colloidal concentrations favor the formation of the multiple-ring pattern; (2) the size of colloidal particles added into DNA aqueous droplets can significantly disrupt smooth multiple rings to form rippled rings and curtain-like periodic patterns with a curious spoke-like structure as the size of colloidal particles increases; and (3) the enhancement of DNA-colloid interaction by oppositely charged colloidal particles results in considerably high irregularity of DNA stain ring spacing. We examine the disruption of the multiring morphology under varied conditions and attribute it to local hydrodynamics governed by colloid aggregation and sedimentation. Our results demonstrate the feasibility of fabricating periodic self-assembled hybrid structures via one-step evaporation of droplets consisting of multiple components.

Dynamic positioning of the fission yeast cell division plane

A key question in cytokinesis is how the cell division plane is positioned. Whereas microtubules of the mitotic apparatus specify the division site in animal cells, we show here that the nucleus plays this role in the fission yeast Schizosaccharomyces pombe. By centrifuging cells to move the nucleus, we find that the nucleus (or a nuclear-associated structure) actively influences the position of contractile ring assembly during early mitosis. Displacement of the nucleus during this induction period can lead to formation of multiple rings. The nucleus signals its position in a microtubule-independent manner by emitting the protein mid1p. Furthermore, movement of ring fragments together minimizes formation of multiple division sites. These dynamic mechanisms of ring positioning provide a robust coordination of nuclear and cell division.

Surface Morphology of Drying Latex Films: Multiple Ring Formation

When a drop of aqueous solution containing suspended particles dries, particles accumulate at the contact line. Often the contact line undergoes a sequence of pinning−depinning events with particles accumulating whenever the contact line is pinned. These processes lead to ring formation, the details of which are examined here. In particular, we provide detailed measurements of ring formation as a function of the drop radius and the size of the suspended particles, and we report measurements of the time dependence of the essentially stochastic pinning−depinning cycles of the contact line motion.

Radial spreading of buoyant, surface plumes in coastal waters

Shallow buoyant, surface plumes in coastal waters sometimes develop by nearly radial spreading from a continuous source, such as at a river mouth. Such plumes often display a ring structure where buoyant water is concentrated between fronts at both the leading and trailing edges of the expanding ring. These rings often occur in multiple, concentric forms. A model of the radial, time dependent spreading of a shallow buoyant layer over a motionless, deep ambient layer is developed. It includes fronts as discontinuities and treats the remainder of the plume flow as inviscid, gravitational spreading controlled by nonlinear, internal waves. Calculations by the method of characteristics are presented that show the evolution of a clear ring structure. The combination of rapid spreading in the radial geometry together with reflection of internal waves off the frontal boundary at the plume leading edge is shown to be necessary for ring formation. A mechanism is suggested for the formation of multiple rings through the shear flow instability inherent in radial spreading.