Onset Of Transition Research Articles

Multi-proxy evidence for sea level fall at the onset of the Eocene-Oligocene transition

Continental-scale expansion of the East Antarctic Ice Sheet during the Eocene-Oligocene Transition (EOT) is one of the largest non-linear events in Earth’s climate history. Declining atmospheric carbon dioxide concentrations and orbital variability triggered glacial expansion and strong feedbacks in the climate system. Prominent among these feedbacks was the repartitioning of biogeochemical cycles between the continental shelves and the deep ocean with falling sea level. Here we present multiple proxies from a shallow shelf location that identify a marked regression and an elevated flux of continental-derived organic matter at the earliest stage of the EOT, a time of deep ocean carbonate dissolution and the extinction of oligotrophic phytoplankton groups. We link these observations using an Earth System model, whereby this first regression delivers a pulse of organic carbon to the oceans that could drive the observed patterns of deep ocean dissolution and acts as a transient negative feedback to climate cooling.

Reprogramming of glucose metabolism via PFKFB4 is critical in FGF16-driven invasion of breast cancer cells.

Fibroblast growth factors (FGFs) are expressed in both developing and adult tissues and play important roles in embryogenesis, tissue homeostasis, angiogenesis, and neoplastic transformation. Here, we report the elevated expression of FGF16 in human breast tumor and investigate its potential involvement in breast cancer progression. The onset of epithelial-mesenchymal transition (EMT), a prerequisite for cancer metastasis, was observed in human mammary epithelial cell-line MCF10A by FGF16. Further study unveiled that FGF16 alters mRNA expression of a set of extracellular matrix genes to promote cellular invasion. Cancer cells undergoing EMT often show metabolic alteration to sustain their continuous proliferation and energy-intensive migration. Similarly, FGF16 induced a significant metabolic shift toward aerobic glycolysis. At the molecular level, FGF16 enhanced GLUT3 expression to facilitate glucose transport into cells, which through aerobic glycolysis generates lactate. The bi-functional protein, 6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase 4 (PFKFB4) was found to be a mediator in FGF16-driven glycolysis and subsequent invasion. Furthermore, PFKFB4 was found to play a critical role in promoting lactate-induced cell invasion since silencing PFKFB4 decreased lactate level and rendered the cells less invasive. These findings support potential clinical intervention of any of the members of FGF16-GLUT3-PFKFB4 axis to control the invasion of breast cancer cells.

Tunable morphing of electroactive dielectric-elastomer balloons

Designing smart devices with tunable shapes has important applications in industrial manufacture. In this paper, we investigate the nonlinear deformation and the morphological transitions between buckling, necking and snap-through instabilities of layered dielectric elastomer (DE) balloons in response to an applied radial voltage and an inner pressure. We propose a general mathematical theory of nonlinear electro-elasticity able to account for finite inhomogeneous strains provoked by the electro-mechanical coupling. We investigate the onsets of morphological transitions of the spherically symmetric balloons using the surface impedance matrix method. Moreover, we study the nonlinear evolution of the bifurcated branches through finite-element numerical simulations. Our analysis demonstrates the possibility to design tunable DE spheres, where the onset of buckling and necking can be controlled by geometrical and mechanical properties of the passive elastic layers. Relevant applications include soft robotics and mechanical actuators.

Effect of local wall temperature on hypersonic boundary layer stability and transition

Wall temperature significantly affects stability and receptivity of the boundary layer. Changing the wall temperature locally may therefore be an effective laminar flow control technique. However, the situation is complicated when the wall temperature distribution is nonuniform, and researchers have experimentally found that local wall cooling may delay the onset of transition. We attempt to clarify the physical mechanisms whereby the local wall temperature affects the transition and the stability of a hypersonic boundary layer. A numerical investigation of the disturbance evolution in a Mach-6 sharp cone boundary layer with local wall heating or cooling is conducted. Direct numerical simulation (DNS) is performed for the single-frequency and broadband disturbance evolution caused by random forcing. We vary the local wall temperature and the location of heating/cooling, and then use the e N method to estimate the transition onset. Our results show that local wall cooling amplifies high-frequency unstable waves while stabilizing low-frequency unstable waves, with local heating amplifying all unstable waves locally. The disturbance amplitude and second-mode peak frequency obtained by DNS agree well with the previous experimental results. Local cooling/heating has a dual effect on the stability of the hypersonic boundary layer. For local cooling, while it effectively inhibits the growth of the low-frequency unstable waves that dominate the transition downstream, it also further destabilizes the downstream flow. In addition, while upstream cooling can delay the transition, excessive cooling may promote it; local heating always slightly promotes the transition. Finally, recommendations are given for practical engineering applications based on the present results.

Investigation of influence of local cooling/heating on nonlinear instability of high-speed boundary layer with direct numerical simulations

The influence of local cooling/heating on two types of nonlinear instabilities of the high-speed boundary layer, namely, the First and Second Mode Oblique Breakdown (FMOB and SMOB), is studied using direct numerical simulations. Local cooling and heating are performed at the weak and strong nonlinear stages of the two types of nonlinear instabilities. It is found that for the FMOB, local cooling at the weak nonlinear region will suppress the increase of the fundamental mode, leading to transition delay. Opposite to local cooling, local heating at the weak nonlinear region of the FMOB will promote the growth of the fundamental mode, resulting in the occurrence of more upstream transition onset. However, if local cooling and heating are performed at the strong nonlinear region, the influence of both local cooling and heating on the FMOB can be neglected. Remarkably, both local heating and cooling can delay the SMOB for different mechanisms. Performing local cooling at the weak nonlinear region of the SMOB, the low amplitude of higher spanwise wavenumber steady mode caused by local cooling lies behind transition delay. When local cooling is set at the strong nonlinear region, the low amplitude of harmonic modes around the cooling area can cause transition delay. Additionally, local heating will suppress the SMOB for the slowing amplification rate of various modes caused by the local heating at both the weak and strong nonlinear stages of the SMOB.

Development of modulation, pairing mechanism, and slip system with optimum vanadium substitution at Bi-sites in Bi-2212 ceramic structure

Present study focuses extensively on the change in electrical, superconducting and microhardness parameters with partial substitution of trivalent V+3 impurities replacing Bi+3 ions in Bi-2212 ceramic compound with the aid of dc electrical resistivity and microhardness test measurements. Experimental findings, calculation results, and phenomenological discussions provide that the optimum vanadium substitution level is found to be x = 0.01 in the Bi2.0-xVxSr2.0Ca1.1Cu2.0Oy (Bi-2212) ceramic system for the highest conductivity, crystallinity quality, superconducting, and mechanical performance features depending on the decreased microscopic structural problems. All the findings are wholly verified by scanning electron microscopy (SEM) and X-Ray diffraction (XRD) analyses. The dc electrical measurements indicate that the optimum vanadium ions support the pairing mechanism for the formation of new polaronic states in the clusters of microdomains, and hence expand superconducting energy gap due to the enhancement of amplitude part of pair wave function in the spin-density wave systems. The excess vanadium content degrades all the basic thermodynamics and quantum mechanical quantities mentioned due to the stress-induced phase transformation. Numerically, the Bi-2212 advanced ceramic matrix prepared by the optimum vanadium impurity is noticed to present the smallest residual resistivity value of 0.08 mΩ cm, room temperature resistivity value of 8.84 mΩ cm, and broadening degree of 0.36 K. Similarly, the ceramic material is found to possess the highest residual resistivity ratio of 3.05, carrier concentration number of 0.153041, critical transition offset and onset value of 84.66 K and 85.02 K, respectively. Besides, the microhardness findings reveal that the same compound with the least sensitivity to the applied test loads exhibits the largest Hv value of 4.799 GPa, Young's moduli of 393.303 GPa, yield strength of (0.969 GPa), and elastic stiffness coefficient of 15.5574 (GPa)7/4 under the applied test load of 0.245 N. The XRD investigations show that the presence of optimum vanadium impurity supports the formation of a high superconducting phase, c-axis length, and average crystallite size. All the findings are morphologically confirmed by the SEM images. It is found that the crystallographically best crystallinity quality and view of surface morphology is observed for the optimum vanadium substitution level. All in all, new higher properties for the conductivity, crystallinity quality, surface morphology, superconducting, and microhardness parameters based on the optimum vanadium replacement encourage the Bi-2212 crystal system to use in much more application places.

An analysis tool for boundary layer and correlation-based transition onset assessment on generic geometries

AbstractToday’s CFD simulations tools and the related computational resources provide engineers an enormously high-fidelity design tool to generate an enormous aerodynamic and aerothermal database, for both the laminar and turbulent state, in a short time span. However, transitional flow simulation is still in its infancy that one still needs to rely on practical engineering correlations composed of typical boundary-layer parameters. This work describes the methodology to extract necessary parameters and profile information of the local boundary layer from any vast simulation dataset in an automatic fashion, allowing to apply a huge variety of best-practise correlations for transition prediction relying on local quantities on any type of 3D geometric body. The validation on a simple test case of a flat plate and application to a representative and complex use cases with the geometry of the HEXAFLY-INT hypersonic glider demonstrate the potential of this engineering methodology.

Multimerizations, Aggregation, and Transfer Reactions of Small Numbers of Molecules.

Chemical equilibria of multimerizations in systems with small numbers of particles exhibit a behavior seemingly at odds with that observed macroscopically. In this paper, we apply the recently proposed expression of equilibrium constant for binding, which includes cross-correlations in reactants' concentrations, to write an equilibrium constant for the formation of clusters larger than two (e.g., trimer, tetramer, and pentamer) as series of two-body reactions. Results obtained by molecular dynamics simulations demonstrate that the value of this expression is constant for all concentrations and system sizes, as well as at an onset of a phase transition to an aggregated state, where densities in the system change discontinuously. In contrast, the value of the commonly utilized expression of equilibrium constant, which ignores correlations, is not constant and its variations can reach few orders of magnitude. Considering different paths for the same multimer formation, with elementary reactions of any order, yields different expressions for the equilibrium constant, yet, with exactly the same value. This is also true for routes with essentially zero probability to occur. Existence of different expressions for the same equilibrium constant imposes equalities between averages of correlated, along with uncorrelated, concentrations of participating species. Moreover, a relation between an average particle number and relative fluctuations derived for two-body reactions is found to be obeyed here as well despite couplings to additional equilibrium reactions in the system. Analyses of transfer reactions, where association and dissociation events take place on both sides of the chemical equation, further indicate the necessity to include cross-correlations in the expression of the equilibrium constant. However, in this case, the magnitudes of discrepancies of the uncorrelated expression are smaller, likely because of partial cancellation of correlations, which exist on both the reactant and product sides.

The effect of leading-edge shape on separation-induced transition on the suction surface of a controlled-diffusion airfoil

To investigate the effect of leading-edge shape on separation-induced transition on suction surface, a large eddy simulation is performed on two compressor controlled-diffusion airfoils: a conventional one with an elliptical leading edge and an optimized one with a curvature-continuous design based on the B-spline description. The Reynolds number based on inflow velocity and chord length is 4.5×105. The critical angle of attack +4°, over which the aerodynamic loss rises sharply, is chosen for simulation. Two transitions are observed on the suction surface, one near the leading edge and the other at 40% chord length. The primary difference between the two airfoils lies in the leading-edge transition, which also leads to the distinction of fluctuating velocity amplitude and energy loss in the subsequent development of boundary layer flow. In order to provide an insight into the transition mechanism, the frequency spectrum analysis is conducted, and the results indicate that the amplification of disturbances during transition is dominated by Kelvin–Helmholtz instability. The mechanisms of energy transport and dissipation are analyzed, and the influence of leading-edge curvature on the initial state of boundary layer flow is elucidated from a dynamic perspective. The results show that continuous and large curvature distributions are more conducive to suppressing the formation of leading-edge separation bubble and delaying the onset of transition.

Simplified Stability-Based Transition Transport Modeling for Unstructured Computational Fluid Dynamics

Inspired by the model framework, a new -based model was developed and implemented into an unstructured Reynolds-averaged Navier–Stokes (RANS) code. The new model applies a modified version of the -transport equation of the model. This new implementation applies an alternative local formulation for the pressure-gradient parameter that allows the local assessment of the transition criterion within the boundary layer and, thereby, simplifies the model and increases the accuracy of the transition onset location. The resulting prediction approach is robust, user-friendly, and suitable for unstructured RANS solvers with high parallelization. To attain a wide application range of the prediction method, while keeping the simplicity of the approach, a physical path-independent transition criterion was adopted, which was calibrated based on linear stability theory results. The approach was successfully validated against experimental data for various relevant test cases. In addition, results were also compared with results obtained with the model and, for some cases, with the method, which showed a strong similarity in the predictions of the method and the new model.

Morphological, Functional, and Physico‐Chemical Properties of Non‐Conventional Starch Derived from Discarded Immature Apples

AbstractThe starch yield of 23–28% (db) with 35–43% amylose content is recovered from different immature apple varieties. Scanning electron microscopy reveals the presence of the dome to spherical shaped granules of 3.1–11.62 µm size. The transition temperatures, onset temperature, peak temperature, conclusion temperature, and enthalpy of gelatinization are calculated using differential scanning calorimetry (DSC) ranges between 61.62 and 64.48 °C, between 64.61 and 68.07 °C, between 68.64 and 72.37 °C, and between 4.35 and 17.49 J g−1, respectively. The water absorption capacity and oil absorption capacity of starches range between 1.036 and 1.372 mL g−1 and between 0.876 and 1.125 mL g−1, respectively. The peak viscosity of 638–1942 cP is achieved in 3.8–6.10 min at a pasting temperature of 65–71 °C. A yield stress of 10–39 Pa is sufficient to instigate the Herschel Bulkley flow. The paste of Mollie's Delicious starch is more structured and elastic; its gel has a hardness of 3.5 N and maximum recovery strength.

Study of Structure and Phase Transformations in Rejuvenated Rapidly Quenched TiNiCu Alloys

Alloys of the quasibinary TiNi-TiCu system manufactured by melt quenching in the form of thin 20–50 μm ribbons have proven to show good potential as materials for the fabrication of micromechanical devices. At high cooling rates (about 106 K/s), this method allows producing high-copper (more than 20 at.%) amorphous alloys which exhibit an excellent shape-memory effect after crystallization. Their properties are known to largely depend on the crystallization conditions and the structure of the initial amorphous material acting as a precursor for the formation of crystal phases. It has been shown recently that the rejuvenation procedure (cryogenic thermocycling) of metallic glasses is one of the most promising methods of improving their properties. In this study, we investigated for the first time the effect of cryogenic thermocycling of rapidly quenched amorphous TiNiCu on the initial state, as well as on structure formation and the phase transformation patterns of subsequent crystallization conducted using various methods. The effect was analyzed utilizing the methods of scanning and transmission electron microscopy, X-ray diffraction analysis, and differential scanning calorimetry. The results show that rejuvenation treatment slightly reduces the glass transition and crystallization onset temperatures and moderately changes the sizes of structural features (grains, martensite plates), the quantity of the martensite phase, and the characteristic temperatures and enthalpy of the martensitic transformation.

Observation of c -axis magnetization at low temperatures in the weak ferromagnet FeBO3 reveals a spin-reorientation transition

The weak ferromagnet $\mathrm{Fe}{\mathrm{BO}}_{3}$ is well known for being a unique system for modeling and testing magnetic dynamics primarily due to relatively simple and localized magnetic structure and its interesting spin wave dynamics. At room temperature, it has slightly canted iron moments lying in the $a\text{\ensuremath{-}}b$ plane that result in a strong antiferromagnetic moment and a weak ferromagnetic moment, which results in pronounced ferromagnetic and antiferromagnetic spin modes. However, some previous studies have shown unusual low-temperature behavior that suggests a phase transition. By performing low-temperature magnetization measurements, both in bulk and on the mesoscale, we have observed a low-temperature magnetic texture in this material in which a large $c$-axis magnetization occurs. Magnetic fields along the $c$ axis as high as 1300 Oe were observed close to the sample's surface. This presents evidence for the onset of a Morin transition or another type of spin-reorientation phase transition wherein the ${\mathrm{Fe}}^{3+}$ moments would acquire a $c$-axis component to their canting below a critical temperature. The observation of this $c$-axis magnetization suggests that there is a different ground state in this material than has been previously expected and could be due to as yet unexplored intricacies of the Dzyaloshinskii-Moriya interaction.

Thermo-Hydraulic Performance of Spring Tape Inserts in a Circular Channel in Transitional Flow Regime

In this work, forced convection experiments were carried out to investigate the variation of heat transfer and pressure drop inside a uniformly heated circular duct fitted with full-length spring tape inserts of varying spring ratios in a transition flow regime. Air was used as the working fluid medium, and experiments were conducted for three constant heat fluxes of 2, 3, and 4 kW-m−2 with Reynolds numbers varied from 502 to 10936 to cover all three flow regimes. For a plain channel heated with 2 kW/m2 of heat flux, the transition begins at a Reynolds number of 2897 and terminates at a Reynolds number of 3783 which brings the transition Reynolds number width of 886. For the same heat flux, a channel with spring tape having a spring ratio of 3, the transition begins at Reynolds number 661 and ends at 1734 while for the case of spring ratio 5, the transition begins at 1305 and ends at 2226. For constant heat flux conditions, a decrease in the spring ratio results in the early onset of transition and which in turn increased the transition length. Predictive Nusselt number and friction factor correlations for different flow regimes have also been presented.

Supercool exit: Gravitational waves from QCD-triggered conformal symmetry breaking

Classically conformal Standard Model extensions predict an intriguing thermal history of the early universe. In contrast to the common paradigm, the onset of the electroweak phase transition can be significantly delayed while the universe undergoes a period of thermal inflation. Then, a first-order chiral phase transition could not only trigger electroweak symmetry breaking but also initiate the exit from supercooling. To study the dynamics of this scenario, we focus on low-energy quark-based QCD effective models that exhibit a first-order transition. While a large amount of latent heat is naturally involved if thermal inflation ends, we find that a supercooling period prior to the QCD scale considerably enhances the timescale of the transition. This enhancement implies great observational prospects at future gravitational wave observatories. Our results are readily applicable to a wide class of scale-invariant SM extensions, as well as strongly coupled dark sectors.

Geometric conjecture about phase transitions.

As phenomena that necessarily emerge from the collective behavior of interacting particles, phase transitions continue to be difficult to predict using statistical thermodynamics. A recent proposal called the topological hypothesis suggests that the existence of a phase transition could perhaps be inferred from changes to the topology of the accessible part of the configuration space. This paper instead suggests that such a topological change is often associated with a dramatic change in the configuration space geometry, and that the geometric change is the actual driver of the phase transition. More precisely, a geometric change that brings about a discontinuity in the mixing time required for an initial probability distribution on the configuration space to reach the steady state is conjectured to be related to the onset of a phase transition in the thermodynamic limit. This conjecture is tested by evaluating the diffusion diameter and ε-mixing time of the configuration spaces of hard-disk and hard-sphere systems of increasing size. Explicit geometries are constructed for the configuration spaces of these systems and numerical evidence suggests that a discontinuity in the ε-mixing time coincides with the solid-fluid phase transition in the thermodynamic limit.

Numerical study of transverse hydrogen injection in high-speed reacting crossflow

A high-speed compressible solver capable of solving detailed chemical reaction mechanisms is developed by coupling the open-source computational fluid dynamic toolbox OpenFOAM® and Cantera 2.5.0. A sonic hydrogen jet discharging from a circular injector into a high enthalpy supersonic crossflow over a flat plate is selected as a test case for the developed solver. The incoming boundary layer is laminar, and an adverse pressure gradient-induced transition is expected due to transverse injection. The test case is selected to serve two purposes. First, to validate the developed solver. Second, to inspect the capability of Reynolds-Averaged Navier–Stokes (RANS) in predicting the flame characteristics in high-speed flows involving laminar to turbulent transition. The present study features three-dimensional RANS simulations with Shear Stress Transport (SST) k–ω and Langtry–Menter SST k–ω turbulence models, with three values of inlet turbulent intensity: I = 0.5, 1, and 2. Analysis showed that laminar to turbulent transition plays a significant role in the resulting flame structure. A fully turbulent SST k–ω model showed several discrepancies from the experiment, especially near the boundary layer. On the other hand, the Langtry–Menter SST k–ω model predicts transition onset and hence the flame structures accurately. Furthermore, the transition onset and the flame structure strongly depend on I. The low-velocity recirculation regions near the injector aid in flame stabilization upstream of the injector. At the same time, the horseshoe vortex dictates the flame spread in a spanwise direction. The reflected shock–boundary layer interaction helps in flame stabilization downstream of the injector.

Chapman–Jouguet deflagration criteria and compressibility dynamics of turbulent fast flames for turbulence-induced deflagration-to-detonation transition

This work characterizes the compressibility dynamics in turbulent fast flames for a range of turbulent flame speeds. These turbulent fast flames experience increased effects of compressibility through the formation of strong shocks and may develop a runaway acceleration combined with a pressure buildup that leads to turbulence induced deflagration-to-detonation transition (tDDT). Simultaneous high-speed particle image velocimetry, OH* chemiluminescence, schlieren, and pressure measurements are used to examine the reacting flow field and flame dynamics. We examine flames with turbulent flame speeds ranging from 100 to 600 m/s. At lower turbulent flame speeds, the flame is not able to produce favorable background conditions for deflagration-to-detonation transition (DDT) onset, and thus flame compressibility and turbulence amplification are less dominant, resulting in a weaker acoustic coupling between the flame and compressed region. As the turbulent burning velocities exceed the Chapman–Jouguet deflagration speed, favorable background conditions are produced, as we observe flame-generated shocks and flame-generated turbulence with higher turbulent velocities and larger turbulent scales. At this regime, the flame is categorized to be at the runaway transition regime that leads to tDDT.

Cellularity and self-similarity of hydrogen expanding spherical flames at high pressures

The onset of transition to cellularity and self-similar propagation of centrally ignited, expanding spherical flames in a reactive environment of H2/O2/N2 and H2/O2/He mixtures at initial pressures up to 15 bar were experimentally investigated using a newly developed, constant-pressure, dual-chamber vessel and were theoretically interpreted based on linear stability theory. The experiments were well-controlled to identify the separate and coupled effects of Darrieus–Landau instability and diffusional–thermal instability. Results show that the critical radius, rcr, for the onset of cellular instability varies non-monotonously with initial pressure for fuel-lean and stoichiometric H2/O2/N2 flames. This non-monotonous pressure dependence of rcr is well captured by linear stability theory for stoichiometric flames. The experimental critical Peclet number, Pecr = rcr/δf, increases non-linearly with the Markstein number, Ma, which measures the intensity of diffusional–thermal instability. However, a linear dependence of Pecr on Ma is predicted by linear stability theory. Specifically, the theory shows well quantitative agreement with the experimental results for mixtures with near-unity Leeff; however, it under-predicts the Pecr for mixtures with off-unity Leeff. In addition, there exists three distinct propagation stages for flames subjected to cellular instability, namely, smooth expansion, transition propagation, and self-similar propagation. The acceleration exponent, α, in the self-similar propagation stage was extracted based on the power-law of drf/dt = αA1/αrf(1 − 1/α), where rf is the instantaneous mean flame radius, and A is a constant. The values of α are located between 1.22 and 1.40, which are smaller than the suggested value (1.5) for self-turbulization.

OCTRA as ultrasonically absorptive thermal protection material for hypersonic transition suppression

Previous investigations in the High Enthalpy Shock Tunnel Göttingen (HEG) of the German Aerospace Center (DLR) show that carbon fiber reinforced carbon ceramic (C/C) surfaces can be utilized to damp hypersonic boundary layer instabilities resulting in a delay of boundary layer transition onset. Numerical stability analyses confirmed these experimental results. However, C/C has some disadvantages, especially the limited oxidation resistance and its low mechanical strength, which could be critical during hypersonic flights. Thus, an ultrasonically absorptive fiber reinforced ceramic material based on a silicon carbide (C/C-SiC) was developed in the past years to fulfill this need. The present paper addresses the numerical rebuilding of the C/C-SiC absorber properties using impedance boundary conditions together with linear stability analysis. The focus of this paper is on the numerical comparison of the original C/C material and the improved C/C-SiC material, referred to as OCTRA in the literature. The influence on the second modes and the transition itself is investigated. The numerical results are compared with HEG wind tunnel tests. The wind tunnel model tested in HEG is a 7^circ half-angle blunted cone with an overall model length of about 1.1 ,textrm{m} and a nose tip radius of 2.5 mm. These experiments were performed at Mach 7.5 and at different freestream unit Reynolds numbers.