Internal Transition Research Articles

Single transition layer in mass-conserving reaction-diffusion systems with bistable nonlinearity

Abstract Mass-conserving reaction-diffusion systems with bistable nonlinearity are useful models for studying cell polarity formation, which is a key process in cell division and differentiation. We rigorously show the existence and stability of stationary solutions with a single internal transition layer in such reaction-diffusion systems under general assumptions by the singular perturbation theory. Moreover, we present a meaningful model for understanding the existence of an unstable transition layer solution; our numerical simulations show that the unstable solution is a separatrix of the dynamics of the model.

Mechanical properties and durability of lightweight cenosphere cementitious composites under coupling effect of dry-wet cycles and salt erosion

Cenospheres are suitable as supplementary cementitious materials to partially replace cement in the production of environmentally friendly lightweight cenosphere cementitious composites (LCCC). In this study, the correlation between the content and particle size of the cenosphere, the early curing system and the performance of LCCC was analyzed. The macroscopic properties and microstructural changes of LCCC under the conditions of dry-wet cycles and salt erosion were studied with different early curing conditions. The durability changes of LCCC mortar under the coupling effect of salt erosion and dry-wet cycles were studied by examining the mass loss rate, relative dynamic modulus of elasticity and salt corrosion resistance coefficient of LCCC mortar. Finally, a comparative analysis of the impact of existing cracks on the performance of LCCC under the coupling effect of dry-wet and salt erosion was conducted. The main innovation of the study includes the mechanical properties and durability of LCCC under dry-wet-salt erosion conditions, as well as the clarification of the impact of prefabricated cracks on the mechanical properties and durability of LCCC. It is found that the flexural strength and the compressive strength of specimens cured at high temperature is generally lower than that of the specimens cured under normal temperature conditions. The wet-dry salt corrosion can exacerbate the erosion the outer shell and inner wall of cenospheres and disrupt the stability of the internal interface transition zone (ITZ) in LCCC. LCCC with CsS exhibits better macroscopic performance and microstructural properties. Pre-existing cracks accelerates the erosion in the cenosphere shell and inner wall under salt solution.

Multidimensional Rietveld refinement of high-pressure neutron diffraction data of PbNCN.

High-pressure neutron powder diffraction data from PbNCN were collected on the high-pressure diffraction beamline SNAP located at the Spallation Neutron Source (SNS) of Oak Ridge National Laboratory (Tennessee, USA). The diffraction data were analyzed using the novel method of multidimensional (two dimensions for now, potentially more in the future) Rietveld refinement and, for comparison, employing the conventional Rietveld method. To achieve two-dimensional analysis, a detailed description of the SNAP instrument characteristics was created, serving as an instrument parameter file, and then yielding both cell and spatial parameters as refined under pressure for the first time for solid-state cyanamides/carbodi-imides. The bulk modulus B 0 = 25.1 (15) GPa and its derivative B'0 = 11.1 (8) were extracted for PbNCN following the Vinet equation of state. Surprisingly, an internal transition was observed beyond 2.0 (2) GPa, resulting from switching the bond multiplicities (and bending direction) of the NCN2- complex anion. The results were corroborated using electronic structure calculation from first principles, highlighting both local structural and chemical bonding details.

Multi-hole liquid CO2 flashing jet: A novel method for achieving trade-off between impact region and impact force through phase transition

A novel multi-hole liquid CO2 flashing jet for coalbed methane exploitation is proposed, which undergoes phase transition during the injection of superheated CO2. The thermal stress generated during the phase-transition process is beneficial for rock fragmentation. Different types of nozzles were compared, and a conical convergent nozzle was selected owing to its wider jets. The proposed jet interaction criteria based on the fuel were examined using CO2, and discrepancies due to the internal phase transition and stronger cooling effects were observed. Nozzles with larger drilling angles were found to be more prone to transition from cone-shaped to jet-shaped morphologies. Coal-breaking experiments were also performed, and three distinct coal-breaking patterns induced by multi-hole flashing CO2 jets were identified. The effects of thermal stress on rock-breaking were evaluated using a beam-scanning electron microscope and wave velocity measurement with a piezoelectric accelerometer. Thermal cracks induced by matrix contraction were identified, indicating the potential to enhance breakage efficiency. The results indicate that the trade-off between the impact region and impact force should be carefully adjusted to achieve the desired coal-breaking performance. This study provides a potential method to utilize CO2, as well as some guidance for the issues that must be addressed in energy exploration using CO2.

Influence of internal bypass conditions on the double bypass matching characteristics of variable cycle high-pressure compression system

The variable cycle high-pressure compression system (VCHCS) consists of a core driven fan stage (CDFS) and a high-pressure compressor (HPC), which are crucial components for controlling the variable cycle engine's bypass ratio. However, the double bypass (DB) matching mechanism of the VCHCS remains insufficiently understood. This study focuses on investigating the DB matching characteristics of the VCHCS under different representative internal bypass conditions. The findings demonstrate that as the internal bypass conditions transition from near choke to near stall, the external bypass stability margin of the VCHCS decreases progressively, and the external bypass characteristic curve of the HPC exhibits an approximate “counter-clockwise rotation” pattern. Furthermore, the operating state of the CDFS and the redistribution of internal and external bypass flow rate, collectively determine the matching state of the compressor system. Building upon the aforementioned summarization regarding the impact of internal bypass conditions on the matching characteristics of the VCHCS, this research integrates flow field analysis to explicate the mechanism of stall under typical operating conditions. The investigation reveals that, when the internal bypass condition under design point and the external bypass condition approaches the stall boundary, an excessive accumulation of low-energy fluid occurs at the external bypass outlet guide vane, subsequently triggers the occurrence of stall. Specifically, when the internal bypass conditions under the near stall point, the predominant limitation on further elevation or reduction of external bypass back pressure lies in the extensive blockage of a massive low-energy fluid on the suction surface of the HPC second stage stator.

Visual depiction and numerical characterization of intricate flow in triply periodic minimal surface foams

Benefiting from the structural specificity and programmability, the bioinspired triply periodic minimal surfaces (TPMSs) bring excellent physicochemical properties that are distinct from conventional topologies. Especially with the rapid development of additive manufacturing and high-performance computing capacities, function-oriented design and synthesis of smart TPMS materials or devices have become feasible. Therefore, understanding the flow characterizations induced by TPMS foams is of remarkable importance to the successful design and practical operation. However, the in-depth studies and theoretical guidance on the relationship between structure and flow characterizations of TPMS foams are still limited. In this study, an Eulerian and Lagrangian coupled model is developed to investigate the internal flow behaviors and flow regime transition mechanism from creeping to inertial flow in four representative TPMS foams. The simulation accuracy is then validated by a high-resolution pore-scale flow field observation. Results show that the flow morphology and pressure drop characteristics are highly influenced by TPMS geometry and Re. Among which, Schwarz Diamond (D), Schoen Gyroid (G), and Fischer-Koch S (S) foams are more susceptible to radial flow disturbance, while Schoen inverted Weissenberg periodic foam to axial flow disturbance. In addition, higher porosities delay the transition to transitional regime of the flow. This work establishes firm theoretical and methodological foundations for the customization and intelligent development of bioinspired TPMS foam materials in broad fluidic applications.

Waddington landscape for prototype learning in generalized Hopfield networks

Networks in machine learning offer examples of complex high-dimensional dynamical systems inspired by and reminiscent of biological systems. Here, we study the learning dynamics of generalized Hopfield networks, which permit visualization of internal memories. These networks have been shown to proceed through a “feature-to-prototype” transition, as the strength of network nonlinearity is increased, wherein the learned, or terminal, states of internal memories transition from mixed to pure states. Focusing on the prototype learning dynamics of the internal memories, we observe stereotypical dynamics of memories wherein similar subgroups of memories sequentially split at well-defined saddles. The splitting order is interpretable and reproducible from one simulation to the other. The dynamics prior to splits are robust to variations in many features of the system. To develop a more rigorous understanding of these global dynamics, we study smaller subsystems that exhibit similar properties to the full system. Within these smaller systems, we combine analytical calculations with numerical simulations to study the dynamics of the feature-to-prototype transition, and the emergence of saddle points in the learning landscape. We exhibit regimes where saddles appear and disappear through saddle-node bifurcations, qualitatively changing the distribution of learned memories as the strength of the nonlinearity is varied—allowing us to systematically investigate the mechanisms that underlie the emergence of the learning dynamics. Several features of the learning dynamics are reminiscent of the Waddington's caricature of cellular differentiation, and we attempt to make this analogy more precise. Memories can thus differentiate in a predictive and controlled way, revealing bridges between experimental biology, dynamical systems theory, and machine learning. Published by the American Physical Society 2024

Lyotropic Liquid Crystalline Phase Nanostructure and Cholesterol Enhance Lipid Nanoparticle Mediated mRNA Transfection in Macrophages

AbstractMacrophages are unique immune cells attracting growing attention as a potential candidate for cell‐based therapy for infectious diseases and cancer. Strategies that can reprogramme or gene‐edit macrophages hold potential across a spectrum of acute and chronic conditions. Herein, lipid nanoparticles (LNPs) are developed containing the ionizable lipid SM‐102, helper lipid monoolein which is known for self‐assembly in aqueous solutions into the inverse cubic lyotropic liquid crystalline mesophase, and cholesterol as an mRNA nanocarrier. The immortalized alveolar macrophage cell line (MH‐S cells) is utilized to investigate how cholesterol concentration impacts on mRNA delivery which is further validated using primary mouse alveolar macrophages isolated from the bronchoalveolar compartment and human monocyte derived macrophages. By using high‐throughput synchrotron small angle X‐ray scattering (SAXS), an acidification‐induced non‐ordered to ordered internal nanostructure transition of the formulated LNPs is observed, following the transition sequence of inverse micellar to hexagonal to cubic mesophase in the pH range from 7 to 4. Cholesterol is identified as another crucial component for superior mRNA transfection in macrophages, contributing to nanostructure transition and protein corona variation. Successful ex vivo mRNA transfection is also achieved in primary macrophages, highlighting the prospectivity of reprogramming macrophages as a cell therapy for lung diseases.

Risks of Ecosystems’ Degradation: Portuguese Healthcare Professionals’ Mental Health, Hope and Resilient Coping

Healthcare professionals constantly face situations that reflect ecosystems’ degradation. These can negatively affect their mental health. Research suggests that hope and resilience can play an important role in this scenario, since they are related to/predict mental health in highly heterogeneous samples (considering geography, age, profession, health, etc.). In this context, the aims of the present study are the following: to characterize and explore the relationship between hope, resilient coping and mental health in Portuguese healthcare professionals. Using Google Forms, 276 healthcare professionals answered the GHQ-28, the (adult) Trait Hope Scale, and the Brief Resilient Coping Scale (retrospective, analytical observational, cross-sectional, descriptive and correlational research design). The minimum and maximum possible scores were reached, with the exception of the maximum score of GHQ-28-Total. Regarding Hope, 19.6% scored below the midpoint (M = 43.46, SD = 11.97); 29.3% revealed low resilience (M = 14.93, SD = 4.05); and the average of four of the five Mental Health scores (exception: Severe depression) indicates the probability of a psychiatric case. Hope correlated with Social dysfunction and GHQ-28-Total; resilient coping proved to be a (weak) predictor of four of the five GHQ-28 indicators (exception: Severe depression). The results support the need to promote the sample’s mental health, hope and resilient coping. They also suggest that stimulating resilient coping may contribute to improving healthcare professionals’ mental health. Prior research (e.g., on therapies to enhance hope, resilience and, thus, mental health), to which the current study contributes, supports optimism towards the necessary internal sustainability transition.

Excitation-Dependent Emission in Sb3+-Doped All-Inorganic Rare-Earth Double Perovskites for Anticounterfeiting Applications.

Achieving high-efficiency tunable emission in a single phosphor remains a significant challenge. Herein, we report a series of Sb3+-doped all-inorganic double perovskites, Sb3+:Cs2NaScCl6, with efficient excitation-dependent emission. In 0.5%Sb3+:Cs2NaScCl6, strong blue emission with a high photoluminescence quantum yield (PLQY) of 85% is obtained under 265 nm light irradiation, which turns into bright neutral white light with a PLQY of 56% when excited at 303 nm. Spectroscopic and computational investigations were performed to reveal the mechanism of this excitation-dependent emission. Sb3+ doping induces two different excitation channels: the internal transition of Sb3+: 5s2 → 5s5p and the electron transfer transition of Sb3+: 5s → Sc3+ 3d. The former one generates excited Sb3+ ions, which can undergo efficient energy transfer to populate the host self-trapped exciton (STE) state, yielding enhanced blue emission. The latter one leads to the formation of a new STE state with the hole localized on Sb3+ and the electron delocalized on the nearest Sc3+, which accounts for the newly exhibited low-energy emission. The difference in the excitation pathways of the two emitting STE states results in the highly efficient excitation-dependent emission, making the doped systems promising anticounterfeiting materials.

Synthesis and luminescent properties of cellulose acetate butyrate films doped with europium complex Eu(TTA)3 for optical thermometry

In this work, the luminescent β-diketonate europium complex, Eu(TTA)3, was incorporated into the polymer cellulose acetate butyrate in different concentrations in the form of composite films. The photoluminescence analysis showed that the composites improved the internal transition of the europium ion, 5D0 → 7F2, mainly responsible for the emission of red light from the complex, by providing a highly asymmetric chemical environment around the europium ion and by reducing non-radiative decays. The composite matrix also contributed to the quantum efficiency of the luminescence, reaching 38 %, by reducing the excited state deactivation rates. The luminescence lifetime of the composite linearly decayed with increasing temperature, while the luminescence intensity displayed an exponential decrease by increasing temperature, both behaviors proved to be appropriate for use in optical thermometry. The analysis of Raman spectra, Judd-Ofelt parameters, decay rates, and lifetime showed that the characteristics of the isolated complex were mostly maintained after being added to the polymeric matrix.

Pareto efficiency of infinite-horizon cooperative stochastic differential games with Markov jumps and Poisson jumps

This paper investigates a wide class of infinite-horizon cooperative stochastic differential games with Markov jumps and Poisson jumps, which can model uncertainties of internal mode transition and characterize occasional sudden changes in the games, respectively. Firstly, the necessary conditions which guarantee the existence of Pareto solutions are obtained by utilizing the Lagrange multiplier method and the stochastic maximum principle with Markov jumps and Poisson jumps. Then the sufficient conditions which guarantee the existence of Pareto efficient strategies are derived. Secondly, the well-posedness of cooperative stochastic differential games (CSDG) with Markov jumps and Poisson jumps in infinite horizon is established when the solution of generalized algebraic Riccati equation (GARE) exists. Furthermore, we can obtain Pareto solutions by introducing the coupled algebraic Lyapunov equations (ALEs). Finally, the numerical examples verify the theoretical results.

A multi-frequency ultrasonic method for nondestructive detection of setting times and internal structure transition of building materials

Setting times of building materials are crucial factors in the construction industry, as they directly affect the construction process. Accurate determination of setting times is essential to ensure that construction materials meet design requirements before demolding. This study introduces a new method using longitudinal waves with multi-frequencies to nondestructively determine the setting times of building materials. The measurement performance was examined by comparing the wave velocity with the results obtained using Vicat and calorimetry methods. A broad range of frequencies was applied to capture the transition of particle size and phase densification during the hardening process. The results showed that the collected data, including SEM images, and formation/transformation of chemical structures, supported the high accuracy in measuring the setting times via velocity regardless of sample type and hardness condition. Furthermore, by utilizing multi-frequencies, the proposed setup improved the detection sensitivity, capable of quantitatively monitoring the modification of internal structures during the monitoring period.

Preparation, Characterization, and Biological Activity of La(III), Nd(III), Er(III), Gd(III), and Dy(III) Complexes with Schiff Base Resulted from Reaction of 4-Antipyrinecarboxaldehyde and 2-Aminobenzothiazole

The research includes the preparation of several complexes of the internal transition elements lanthanide (Ln = La, Nd, Er, Gd, and Dy) containing the 4f shell, with Schiff bases resulting from condensation reactions between 4-antipyrinecarboxaldehyde and 2-aminobenzothiazoles. Schiff's base was identified using FTIR spectra, UV-vis spectroscopy, elemental microanalysis CHNSO, nuclear magnetic resonance, mass spectrometry, and TGA thermal analysis. The complexes were studied and identified with elemental microanalysis CHNSO, FTIR spectroscopy, UV-vis spectroscopy, TGA thermal analysis, conductivity measurement, and magnetic sensitivity. The result showed that these complexes were classified as homogeneous bidentate complexes with the general formula of [Ln2(L)2(NO3)6]·6H2O. The physical measurements indicated that the prepared complexes are non-electrolyte and paramagnetic. Some compounds prepared in vitro were evaluated for their antibacterial activity against four types of pathogenic strains Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Klebsiella pneumonia, and using the agar disc spreading method for the evaluation. The results showed that some of these complexes have good antibacterial activity compared to the biological activity of the ligand. Also, the biological activity of Schiff's base and the prepared complexes were evaluated against three types of fungi (Candida albicans, Tropical fungi, and Scandal fungi), and they showed great activity against the prepared complexes.

Triple Adaptation of Constitutional Dynamic Networks of Imines in Response to Micellar Agents: Internal Uptake-Interfacial Localization-Shape Transition.

Understanding the behavior of complex chemical reaction networks and how environmental conditions can modulate their organization as well as the associated outcomes may take advantage of the design of related artificial systems. Microenvironments with defined boundaries are of particular interest for their unique properties and prebiotic significance. Dynamic covalent libraries (DCvLs) and their underlying constitutional dynamic networks (CDNs) have been shown to be appropriate for studying adaptation to several processes, including compartmentalization. However, microcompartments (e.g., micelles) provide specific environments for the selective protection from interfering reactions such as hydrolysis and an enhanced chemical promiscuity due to the interface, governing different processes of network modulation. Different interactions between the micelles and the library constituents lead to dynamic sensing, resulting in different expressions of the network through pattern generation. The constituents integrated into the micelles are protected from hydrolysis and hence preferentially expressed in the network composition at the cost of constitutionally linked members. In the present work, micellar integration was observed for two processes: internal uptake based on hydrophobic forces and interfacial localization relying on attractive electrostatic interactions. The latter drives a complex triple adaptation of the network with feedback on the shape of the self-assembled entity. Our results demonstrate how microcompartments can enforce the expression of constituents of CDNs by reducing the hydrolysis of uptaken members, unravelling processes that govern the response of reactions networks. Such studies open the way toward using DCvLs and CDNs to understand the emergence of complexity within reaction networks by their interactions with microenvironments.

Zircon-to-reidite phase transition enhanced by minor radiation damage: Implications for hypervelocity impacts

Reidite, a high-pressure phase of zircon, is increasingly identified at terrestrial impact sites. Despite its growing recognition, the potential applications for estimating minimum impact pressure face impediments due to existing discrepancies in the condition of zircon-reidite transformation, controversial models governing the transformation mechanism, and unclear effects of pre-existing radiation damage on reidite formation. Here, we show enhanced reidite formation by synchrotron X-ray diffraction, Raman spectroscopy, and transmission electron microscopy analyses of zircon grains that have experienced different alpha-decay doses from U and Th impurities and subsequent pressurization in diamond anvil cells. Below ∼1 × 1018 α-decay events/g, the α-decay-induced isolated point defects in the still crystalline zircon facilitate the minor atomic readjustments required for reidite formation. However, above this dose, the loss of long-range periodicity in severely damaged or even metamict zircon inhibits the transformation. The enhanced reidite formation by minor radiation damage coincides with the more common occurrence of reidite at impact sites for which the precursor zircon has a relatively lower alpha-decay-event dose before the impact event. In addition, the detailed atomic-scale structures of twinned reidite provide unambiguous evidence for a characteristic internal stress-induced martensitic transition. These findings have important implications for interpreting the formation conditions of natural reidite due to the convergence of pressure from the static, shockwave, and natural reidite samples.

Initial Oxidation Behavior of AlCoCrFeNi High-Entropy Coating Produced by Atmospheric Plasma Spraying in the Range of 650 °C to 1000 °C.

As protective coatings for the thermal parts of aero-engines, AlCoCrFeNi coatings have good application prospects. In this study, atmospheric plasma spraying (APS) was used to prepare AlCoCrFeNi high-entropy coatings (HECs), which were oxidized from 650 °C to 1000 °C. The mechanism of the oxide layer formation and the internal phase transition were systematically investigated. The results show that a mixed oxide scale with a laminated structure was formed at the initial stage of oxidation. The redistribution of elements and phase transition occurred in the HECs' matrix; the BCC/B2 structure transformed to Al-Ni ordered B2 phase and Fe-Cr disordered A2 phase.

Internal Transition Layer Structure in the Reaction–Diffusion Problem for the Case of a Balanced Reaction with a Weak Discontinuity

Internal Transition Layer Structure in the Reaction–Diffusion Problem for the Case of a Balanced Reaction with a Weak Discontinuity

Existence and Stability of Solutions with Internal Transition Layer for the Reaction–Diffusion–Advection Equation with a KPZ-Nonlinearity

We study a boundary value problem for a quasilinear reaction–diffusion–advection ordinary differential equation with a KPZ-nonlinearity containing the squared gradient of the unknown function. The noncritical and critical cases of existence of an internal transition layer are considered. An asymptotic approximation to the solution is constructed, and the asymptotics of the transition layer point is determined. Existence theorems are proved using the asymptotic method of differential inequalities, the Lyapunov asymptotic stability of solutions is proved by the narrowing barrier method, and instability theorems are proved with the use of unordered upper and lower solutions.

Judd-Ofelt analysis and NIR spectroscopy properties of Nd3+-doped Na2O/NaF-Al2O3-Y2O3-P2O5 glass and transparent glass-ceramics containing NaYP2O7 crystals

In the present work, the Nd3+-doped Na2O/NaF-Al2O3-Y2O3-P2O5 glass and transparent glass-ceramics were fabricated by conventional melting-quenching and subsequent heat treatment. The glass structure was studied by XRD, DSC, and FTIR spectrum, the fluorophosphate glass exhibits a more compact cross-link network. The UV–Vis–NIR absorption spectra, Judd-Ofelt theory, and photoluminescence spectra were used to explore the absorption and NIR spectroscopic features of the Nd3+-doped phosphate and fluorophosphate glasses. Under the excitation of 582 nm, the intense NIR emission in the Nd3+-doped glasses originating from the internal transition 4F3/2 → 4IJ/2 (J = 13, 11 and 9) was observed, and the transition 4F3/2 → 4I11/2 (1053 nm) is the most dominate. The transparent glass-ceramics (GC) was fabricated via heat treating on the precursor glass (PG) at Tg+100 °C, and the precipitation of NaYP2O7 crystals in GC was confirmed by XRD and SEM. With the benefit of the existence of the NaYP2O7 crystals, the Nd3+-doped GC exhibits higher NIR emission intensity, higher quantum efficiency (72.85% and 84.11%), larger σ(λp) values of 4.24×10-20 cm2 and 4.86×10-20 cm2, larger σ × Δλeff values of 10.22×10-26 cm3 and 11.67×10-26 cm3 than that of PG. These results indicate that the Nd3+-doped phosphate and fluorophosphate glasses and glass-ceramics may be used as a gain medium for 1053 nm laser emission.