Reversal Of Curvature Research Articles

Crown control in a pair of cavitation bubbles close to a free surface: A numerical study

When a cavitation bubble re-expands near the surface of a liquid, an axisymmetric crown forms around the jet that is initially produced. Controlling this crown is essential if the first jet is to be used in engineering applications such as laser-induced transfer (LIT). Herein, we introduce a second cavitation bubble to control the formation and growth of the crown. Numerical simulations were performed using the compressibleInterIsoFoam solver within the open-source platform OpenFOAM, incorporating a geometric volume-of-fluid approach for tracking interfaces. Detailed analysis showed that a reversal in curvature across the concave interface indicates the moment of crown formation, and this is induced by flow focusing during bubble contraction or momentum transfer from a second expansion. In the presence of the second bubble, the crown type can be classified as either enhanced or inhibited in comparison with a single-bubble scenario. The velocity of crown formation, vcf, is defined to describe the crown type, and a parametric study of crown types was conducted based on the dimensionless stand-off distances, γ1 and γ2. The findings of this study offer new insights into the field of LIT.

Mechano-biochemical marine stimulation of inversion, gastrulation, and endomesoderm specification in multicellular Eukaryota.

The evolutionary emergence of the primitive gut in Metazoa is one of the decisive events that conditioned the major evolutionary transition, leading to the origin of animal development. It is thought to have been induced by the specification of the endomesoderm (EM) into the multicellular tissue and its invagination (i.e., gastrulation). However, the biochemical signals underlying the evolutionary emergence of EM specification and gastrulation remain unknown. Herein, we find that hydrodynamic mechanical strains, reminiscent of soft marine flow, trigger active tissue invagination/gastrulation or curvature reversal via a Myo-II-dependent mechanotransductive process in both the metazoan Nematostella vectensis (cnidaria) and the multicellular choanoflagellate Choanoeca flexa. In the latter, our data suggest that the curvature reversal is associated with a sensory-behavioral feeding response. Additionally, like in bilaterian animals, gastrulation in the cnidarian Nematostella vectensis is shown to participate in the biochemical specification of the EM through mechanical activation of the β-catenin pathway via the phosphorylation of Y654-βcatenin. Choanoflagellates are considered the closest living relative to metazoans, and the common ancestor of choanoflagellates and metazoans dates back at least 700 million years. Therefore, the present findings using these evolutionarily distant species suggest that the primitive emergence of the gut in Metazoa may have been initiated in response to marine mechanical stress already in multicellular pre-Metazoa. Then, the evolutionary transition may have been achieved by specifying the EM via a mechanosensitive Y654-βcatenin dependent mechanism, which appeared during early Metazoa evolution and is specifically conserved in all animals.

Estimation of sintering pressure during the pore fragmentation via coordination number and reversal of curvature

Sintering is a process of removing pores from a powder compact, and the pressure to shrink pores is called sintering pressure. In this research, to explain the improvement of sintering in accordance with pore fragmentation, the change in the number of grains per pores (coordination number) was highlighted, and the sintering pressure was expressed and calculated in terms of a coordination number. To this end, variables affecting the sintering, such as grain size, pore size, direction of curvature, and dihedral angle, were expressed as the coordination numbers. Evaluation of the sintering pressure for bimodal pores present in 1 wt.% Al-doped ZnO showed that micron pores were expected to exhibit 21 kPa at the mode size, while submicron pores were evaluated to have 6.3–7.9 MPa. This shows that the pore fragmentation, that can be induced by initial heat treatment under mild external pressure, has the effect of improving the sintering pressure by approximately 300 times.

Reversible Curvature Reversal of Monolithic Liquid Crystal Elastomer Film and Its Smart Valve Application.

Beyond a traditional stimuli-responsive soft actuator that shows a single motion by a stimulus, multidirectional actuation reversal with a single stimulus is highly required in applications such as shape morphing sensors and soft robotics. Liquid crystal elastomers (LCEs) are one of the most attractive candidates for the soft actuator due to their capability of stimuli-responsive shape changing in 3D, which is programmable with local orientation of LC mesogens. Here, a simple but effective method to fabricate monolithic LCE actuators that are capable of reversible curvature reversal in bending and twisting deformation by a single stimulus-heat-is reported. The curvature reversal of the LCE film can be programmed by means of asymmetric crosslinking density along the thickness and the orientation of the LC mesogens. The curvature reversal of the monolithic LCE film exhibits highly reversible (more than 100 times) and fast actuation (≈3-5 s) by heating and cooling, allowing new concept of a practical application using LCE material: a self-regulated smart valve that is capable of qualitatively sorting liquids by temperature. It is believed that this system is potentially applied to a self-regulated sorting platform for various endothermic and exothermic chemical or biological reactions.

Liquid crystal elastomer shells with topological defect-defined actuation: Complex shape morphing, opening/closing, and unidirectional rotation

We produce hollow sphere liquid crystal elastomer (LCE) actuators from a nematic precursor mixture, brought into the shape of a self-closing shell with tangential anchoring of the director field n(r), using a solvent-assisted microfluidic technique. By separating the shell production from the polymerization and cross-linking, the precursor is allowed to approach its equilibrium n(r) configuration in the shell, spontaneously forming topological defects of total strength +2. However, the photopolymerization into an LCE induces a brief but strong distortion of the overall n(r) and the defect configuration, even changing the ground state shape in the case of thick shells. The resulting LCE shells show a rich capacity for reversible shape morphing upon heating and cooling, the exact actuation mode defined by n(r), and the final defect configuration stabilized at the end of polymerization. In regions with a single +1 defect, a reversal of curvature from concave to convex is found, punctured shells exhibit a strong shape change between a nearly closed sphere at low temperature and an open-ended spherocylinder at high temperature, and all shells rotate upon actuation when suspended in a fluid. As the rotation is stronger during relaxation than during actuation, thus breaking the symmetry, the net rotation is unidirectional.

Switch from connection ductility to reinforcement ductility with curvature reversal in timber-concrete composites

While multi-span continuity can be used to structurally enhance timber-concrete composites (TCCs), there has been scant research into the associated nonlinear load responses particularly of the resulting TCC zones under negative curvature. Consequently this paper presents tests to failure of TCC specimens using hardwood laminated veneer lumber joists and steel mesh connectors, one specimen (TP) under positive curvature, the other (TN) under negative curvature. It was found that the mesh connectors enabled high levels of slab-joist interaction not only in TP where the slab was almost uncracked, but also in TN where the slab exhibited pronounced cracking. Such distinct interaction enabled TN and TP to develop more than twice and six times, respectively, the stiffness of the joist acting alone. Both TCC members exhibited encouraging ductility, the source of which switched from connection yield distributed along half the span in TP to steel rebar yield concentrated at midspan in TN. TP displayed deflection (global) and curvature (local) ductility near-plateaux over ranges close to or exceeding the corresponding elastic ranges, while for TN the ductility was manifest as low tangent stiffness regimes over deflection and curvature ranges generously exceeding the corresponding elastic ranges. A conspicuous residual hinge at midspan in TN and significant residual end slip in TP provided visual evidence of the ductility. These observations address the issue of TCC connection effectiveness in cracked concrete that has emerged from updating EC5. Crucially, the ductility of TN is predicated on the hardwood’s high strain to fracture in flexure, which ensured that extensive rebar plasticity preceded failure of the timber.

Pore geometry control of apparent wetting in porous media

Wettability, or preferential affinity of a fluid to a solid substrate in the presence of another fluid, plays a critical role in the statics and dynamics of fluid-fluid displacement in porous media. The complex confined geometry of porous media, however, makes upscaling of microscopic wettability to the macroscale a nontrivial task. Here, we elucidate the contribution of pore geometry in controlling the apparent wettability characteristics of a porous medium. Using direct numerical simulations of fluid-fluid displacement, we study the reversal of interface curvature in a single converging-diverging capillary, and demonstrate the co-existence of concave and convex interfaces in a porous medium—a phenomenon that we also observe in laboratory micromodel experiments. We show that under intermediate contact angles the sign of interface curvature is strongly influenced by the pore geometry. We capture the interplay between surface chemical properties and pore geometry in the form of a dimensionless quantity, the apparent wettability number, which predicts the conditions under which concave and convex interfaces co-exist. Our findings advance the fundamental understanding of wettability in confined geometries, with implications to macroscopic multiphase-flow processes in porous media, from fuel cells to enhanced oil recovery.

Dynamics of jets produced by bursting bubbles

Sea spray is the main source of aerosols above the ocean. One of the pathways for sea spray production is through bubble bursting which ejects myriads of droplets. We present a detailed description of the velocity of jets formed by bubble bursting, obtained through extensive comparison between experimental results and numerical simulations for a wide range of physical parameters. We discuss the importance of the shape of the cavity on the jet velocity and the regime of parameters for which drop ejection is observed. We present a phenomenological formula that predicts the jet velocity for the full range of parameters and compare it to a theoretical prediction based on curvature reversal. The results are then discussed in light of their fundamental applications in the understanding of the phenomena.

Revision of Bubble Bursting: Universal Scaling Laws of Top Jet Drop Size and Speed.

The collapse of a bubble of radius R_{o} at the surface of a liquid generating a liquid jet and a subsequent first drop of radius R is universally scaled using the Ohnesorge number Oh=μ/(ρσR_{o})^{1/2} and a critical value Oh^{*} below which no droplet is ejected; ρ, σ, and μ are the liquid density, surface tension, and viscosity, respectively. First, a flow field analysis at ejection yields the scaling of R with the jet velocity V as R/l_{μ}∼(V/V_{μ})^{-5/3}, where l_{μ}=μ^{2}/(ρσ) and V_{μ}=σ/μ. This resolves the scaling problem of curvature reversal, a prelude to jet formation. In addition, the energy necessary for the ejection of a jet with a volume and averaged velocity proportional to R_{o}R^{2} and V, respectively, comes from the energy excess from the total available surface energy, proportional to σR_{o}^{2}, minus the one dissipated by viscosity, proportional to μ(σR_{o}^{3}/ρ)^{1/2}. Using the scaling variable φ=(Oh^{*}-Oh)Oh^{-2}, it yields V/V_{μ}=k_{v}φ^{-3/4} and R/l_{μ}=k_{d}φ^{5/4}, which collapse published data since 1954 and resolve the scaling of R and V with k_{v}=16, k_{d}=0.6, and Oh^{*}=0.043 when gravity effects are negligible.

Instability of quantum de Sitter spacetime

Quantized fields (e.g., the graviton itself) in de Sitter (dS) spacetime lead to particle production: specifically, we consider a thermal spectrum resulting from the dS (horizon) temperature. The energy required to excite these particles reduces slightly the rate of expansion and eventually modifies the semiclassical spacetime geometry. The resulting manifold no longer has constant curvature nor time reversal invariance, and back-reaction renders the classical dS background unstable to perturbations. In the case of AdS, there exists a global static vacuum state; in this state there is no particle production and the analogous instability does not arise.

Curvature Reversal and Residual Stress in Solid Oxide Fuel Cell Induced by Chemical Shrinkage and Expansion

AbstractStructural stability of layered functional ceramic composites is challenged by curvature effects and residual stresses caused by the thermal mismatch and chemical strains. In this study, a phenomenon of curvature reversal is found in the half‐cell structure of solid oxide fuel cell (SOFC) during the reduction of the half‐cell from NiO‐YSZ to Ni‐YSZ. An analytical model is derived to study the curvature and residual stress caused by the chemical shrinkage and expansion of anode. With reducing to Ni‐YSZ, the curvature of the half‐cell changes from the initial direction to an opposite direction, then back to the initial direction. This curvature reversal is inevitable during reduction while the thickness ratio of electrolyte to anode is between 0 and 0.102. The residual stress in electrolyte, calculated by the analytical model, is well agreement with the experiment result using X‐ray stress analysis. The YSZ layer is always subjected to compressive stress in despite of curvature reversal existing in half‐cell. It is impossible to get the residual stress by measuring the curvature unless the half‐cell was reduced completely.

The counterbend phenomenon in flagellar axonemes and cross-linked filament bundles

Recent observations of flagellar counterbend in sea urchin sperm show that the mechanical induction of curvature in one part of a passive flagellum induces a compensatory countercurvature elsewhere. This apparent paradoxical effect cannot be explained using the standard elastic rod theory of Euler and Bernoulli, or even the more general Cosserat theory of rods. Here, we develop a geometrically exact mechanical model to describe the statics of microtubule bundles that is capable of predicting the curvature reversal events observed in eukaryotic flagella. This is achieved by allowing the interaction of deformations in different material directions, by accounting not only for structural bending, but also for the elastic forces originating from the internal cross-linking mechanics. Large-amplitude static configurations can be described analytically, and an excellent match between the model and the observed counterbend deformation was found. This allowed a simultaneous estimation of multiple sperm flagellum material parameters, namely the cross-linking sliding resistance, the bending stiffness, and the sperm head junction compliance ratio. We further show that small variations on the empirical conditions may induce discrepancies for the evaluation of the flagellar material quantities, so that caution is required when interpreting experiments. Finally, our analysis demonstrates that the counterbend emerges as a fundamental property of sliding resistance in cross-linked filamentous polymer bundles, which also suggests that cross-linking proteins may contribute to the regulation of the flagellar waveform in swimming sperm via counterbend mechanics.

Orthopedic manifestations and implications for individuals with Costello syndrome

Costello syndrome is a rare genetic condition caused by heterozygous alterations in HRAS and characterized by multi-system abnormalities. Individuals with Costello syndrome usually present with severe feeding difficulties in infancy, short stature, coarse facial features, increased tumor risks, cardiac and neurological complications, intellectual disability and orthopedic complications. This study further defines the orthopedic manifestations affecting individuals with Costello syndrome. We studied 43 participants and performed medical records review, clinical examinations and orthopedic inquiry forms. In 23 participants, hip and or spinal imaging assessments were completed. Serial radiographs were analyzed when available. A total of 25 orthopedic manifestations were identified. Ten manifestations were seen in the majority of the participants: hypotonia (87%), ligamentous laxity (85%), scoliosis (63%), kyphosis (58%), characteristic hand deformities (85%), ulnar deviation of the wrist (63%), elbow (55%) and shoulder contractures (65%), tight Achilles tendon (73%), and pes planus (53%). Other characteristics of special note were hip dysplasia (45%), foot deformities requiring surgical intervention (38%) and osteopenia/osteoporosis (47%). We also studied the development of the hips and spine. Uni- or bilateral hip dysplasia was congenital in some, while it developed throughout childhood in others. Spinal involvement included scoliosis, kyphosis, lordosis, and curvature reversal (thoracic lordosis and lumbar kyphosis). Based on these findings, we recommend routine referral to an orthopedic surgeon as well as instituting screening protocols for hips and spine for individuals with Costello syndrome.

Curvature reversal of the circular motion of swimming bacteria probes for slip at solid/liquid interfaces

Download options Please wait... Supplementary files Supplementary information PDF (370K) Article information DOI https://doi.org/10.1039/C3SM51426A Article type Communication Submitted 22 May 2013 Accepted 24 Jul 2013 First published 26 Jul 2013 Download Citation Soft Matter, 2013,9, 9759-9762 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Curvature reversal of the circular motion of swimming bacteria probes for slip at solid/liquid interfaces L. Lemelle, J. Palierne, E. Chatre, C. Vaillant and C. Place, Soft Matter, 2013, 9, 9759 DOI: 10.1039/C3SM51426A To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Laurence Lemelle Jean-François Palierne Elodie Chatre Cédric Vaillant Christophe Place

Bistable composite laminates: Effects of laminate composition on cured shape and response to thermal load

This paper develops a finite element (FE) approach using commercial ANSYS V11.0 software to accurately predict the cured shape of bistable composites by including the influence of manufacturing imperfections, such as resin rich areas and ply-thickness variations. Laminate composition was characterised by optical microscopy and their cured shapes measured using a Peak Motus motion analysis system. The FE model accurately predicts observed differences between laminate curvature in the two stable states. Localised reversal of curvature resulting from through-thickness shear stress is also predicted. Structural response to thermal loading was experimentally characterised showing a temperature dependent deflection rate and a residual curvature caused by non-reversible residual stresses. FE-predictions show good agreement with experiment over the range 20–110 °C. The presented data highlights the importance of manufacturing processes and materials selection in the design of thermally stressed multi-stable composite structures.

Nonlinear Photoresponse of Disordered Elastomers

We model the polarization-dependent photocontractions of polydomain nematic elastomers. Contraction initially arises by light-induced director rotation. At higher light intensity, strain recovers because the local order parameter diminishes. Thus we predict photostrains to be nonmonotonic with light intensity and predict the induction of a negative global order parameter for the system of polydomains. Nonmonotonic strains would give curvature reversal in thick samples. Our model also predicts an elongational strain response to nonpolarized light.

Wetting in the Au–Sn System

The isothermal spreading of liquid Sn on Au substrates was studied over the temperature range of 250–430 °C using the sessile drop technique in a gaseous flux atmosphere. Digital video imaging was used to record the spreading kinetics, and rapid quenching and metallographic cross-sectioning was used to characterize dissolution and compound formation. Observations showed that three temperature/composition regimes gave rise to their own unique spreading behaviors. At low temperatures/Au concentrations, limited spreading was accompanied by nearly complete isothermal solidification. At intermediate temperatures/Au concentrations, rapid spreading and concurrent appearance of a transient intermetallic compound were observed. At higher temperatures/Au concentrations, extensive spreading was observed in the form of a thick film (∼20 μm) supplied by a central dissolution well whose L/V interface undergoes a global curvature reversal. We discuss the contact line mobility and other mechanisms that affect wetting and spreading behaviors: fluid flow, mass transport and metallurgical reaction.

Effect of Cooling Condition on Deformation of Continuously Cast Stainless Steel 304

This work investigated the effect of the cooling condition on the deformation that was found for continuously cast stainless steel 304 slabs. The transient heat-transfer finite element analysis under various cooling conditions yielded temperature distributions within the slab, which were then used for subsequent calculations of the deformed shape. The asymmetric cooling condition in a cooling pit induced non-uniform and asymmetric thermal gradients with elapsed time. The non-zero final deflection and the reversal of curvature for the slab during cooling were attributed to the combined effect of asymmetric temperature profile and inelastic material property. Parametric studies revealed that a slab material of a low thermal conductivity or yield strength resulted in an increase for final deflection. The present analysis explained the physical cause of the deformation reasonably well.

Curvature and Bending Constants for Phosphatidylserine-Containing Membranes

Phosphatidylserine (PS), an anionic phospholipid of significant biological relevance, forms a multilamellar phase in water with net negative surface charge at pH 7.0. In this study we mixed dioleoylPS (DOPS) with reverse hexagonal (HII)-forming phosphatidylethanolamine (DOPE), and used x-ray diffraction and osmotic stress to quantify its spontaneous curvature (1/R0p) and bending modulus (Kcp). The mixtures were stable HII phases from 5 to 30 mol% PS, providing 16 wt% tetradecane (td) was also added to relieve chain-packing stress. The fully hydrated lattice dimension increased with DOPS concentration. Analysis of structural changes gave an apparent R0p for DOPS of +144Å; opposite in sign and relatively flat compared to DOPE (−30Å). Osmotic stress of the HII phases did not detect a significantly different bending modulus (Kcp) for DOPS as compared to DOPE. At pH≤4.0, DOPS (with no td) adopted the HII phase on its own, in agreement with previous results, suggesting a reversal in curvature upon protonation of the serine headgroup. In contrast, when td was present, DOPS/td formed a lamellar phase of limited swelling whose dimension increased with pH. DOPS/DOPE/td mixtures formed HII phases whose dimension increased both with pH and with DOPS content. With tetradecane, estimates put 1/R0p for DOPS at pH 2.1 at zero. Tetradecane apparently affects the degree of dissociation of DOPS at low pH.

Mean-Field Theory Prediction of the Phase Behavior and Phase Structure of Alkyl-Propoxy-Ethoxylate “Graded” Surfactants in Water: Temperature and Electrolyte Effects

A mean-field lattice theory is used to predict electrolyte effects on the temperature−concentration phase behavior and structure of an alkyl-propoxy-ethoxylate surfactant in water. The salt ions are treated as charged species interacting with surfactant segments and water via adjustable Flory−Huggins χ-parameters. The surfactant undergoes thermotropic (rather than lyotropic) transitions with a reversal in curvature (from water continuous to alkyl continuous) upon an increase in temperature. This is attributed to the “graded” nature of the surfactant interactions with water, which originates from the fact that the propoxy and ethoxy groups become progressively more hydrophobic as the temperature increases. The addition of NaCl is found to sharpen the thermotropic phase transitions and to shift them to lower temperatures compared to the salt-free case. The electrolyte effects on the macroscopic phase behavior are reflected in the microscopic information provided by the model on the species volume fraction p...