Initial Transition Research Articles

Velocity gradient analysis of a head-on vortex ring collision

We simulate the head-on collision between vortex rings with circulation Reynolds numbers of 4000 using an adaptive, multiresolution solver based on the lattice Green's function. The simulation fidelity is established with integral metrics representing symmetries and discretization errors. Using the velocity gradient tensor and structural features of local streamlines, we characterize the evolution of the flow with a particular focus on its transition and turbulent decay. Transition is excited by the development of the elliptic instability, which grows during the mutual interaction of the rings as they expand radially at the collision plane. The development of antiparallel secondary vortex filaments along the circumference mediates the proliferation of small-scale turbulence. During turbulent decay, the partitioning of the velocity gradients approaches an equilibrium that is dominated by shearing and agrees well with previous results for forced isotropic turbulence. We also introduce new phase spaces for the velocity gradients that reflect the interplay between shearing and rigid rotation and highlight geometric features of local streamlines. In conjunction with our other analyses, these phase spaces suggest that, while the elliptic instability is the predominant mechanism driving the initial transition, its interplay with other mechanisms, e.g. the Crow instability, becomes more important during turbulent decay. Our analysis also suggests that the geometry-based phase space may be promising for identifying the effects of the elliptic instability and other mechanisms using the structure of local streamlines. Moving forward, characterizing the organization of these mechanisms within vortices and universal features of velocity gradients may aid in modelling turbulent flows.

Fast breakdown process and characteristics diagnosis of nanosecond pin–pin discharge

In this paper, the characteristics of a nanosecond spark discharge with a pin–pin electrode configuration have been systematically studied. Both a streak camera with high temporal resolution and an intensified charge-coupled device (ICCD) camera are employed together to investigate the breakdown and evolution process of the discharge. The formation of initial breakdown and mode transition from streamer to spark in the electrode gap are clearly observed on the time scale of several nanoseconds with a temporal resolution of 100 ps. In addition, the time-resolved spectra technology is also used to analyze the generation and quenching mechanisms of reactive species, the electron density, and the electron temperature. The results show that there is a 1.25 ns initial discharge breakdown and that a bright cathode spot exists before the transformation from streamer to spark channel. After a faster cathode filament and a slower anode filament propagate and merge at the electrode gap, the spark discharge phase begins. The generation processes of different reactive species depend on the discharge phase to a great extent. The N2* is first generated during the streamer phase while the O*, N*, and N+ are mainly generated under the spark phase, in which the electron temperature calculated by Boltzmann plots is 2.74 eV, and the electron density determined from the Stark broadening of O lines is on the order of 1016 cm−3.

Three Levels of Authoritarian Legitimacy

Who does a personalist authoritarian ruler designate as their successor, and what makes the transition of presidency to them peaceful in the short term? This article argues that these questions can be fruitfully approached from the perspective of political legitimacy, thus contributing to the further conceptualization of legitimacy in autocracies. By analyzing the 2019 leadership succession in Kazakhstan, the article develops a model of multi-level legitimacy that differentiates between three interconnected levels of legitimacy enjoyed by political actors among the general population, the elite, and the international community. The article tracks the legitimation process and the estimated level of legitimacy of three key political actors (Nazarbaev, Tokaev, and Nazarbaeva) from the immediate pre-resignation period until the political crisis of January 2022, covering both phases of succession: Nazarbaev’s exit from and Tokaev’s entry to power. To estimate the actors’ level of legitimacy on the three analytical levels of the model, the article draws from a diverse dataset consisting of public opinion polls, expert commentary, and international actors’ statements. The article finds that in the initial transition process, the estimated level of legitimacy enjoyed by both Nazarbaev and Tokaev was relatively high in all three levels, in contrast to Nazarbaeva’s. It argues that Nazarbaev’s and Tokaev’s legitimacy contributed to the transition’s initial peaceful nature, but Nazarbaeva’s legitimacy deficit resulted in her marginalization in the succession process. The political turmoil of January 2022 demonstrates that a succession that is peaceful in the short term can paradoxically contain the seeds of a succession conflict erupting later.

Abstract C056: The initiation and progression of pancreatic ductal adenocarcinoma through a p53 lens

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease with a 5-year survival rate of only 11%. Slated to be the 2nd most deadly cancer by 2026, pancreatic cancer survival rates have not improved substantially over the years. With a lack of early detection methods and a highly immunosuppressive tumor microenvironment (TME), PDAC tumors are highly resistant to treatment. Oncogenic mutations in KRAS are present in >90% of cases and mutations in the tumor suppressor gene TP53 are present in ~72% of cases. However, why p53 mutations are so prevalent and how they enhance PDAC development is not well understood. To elucidate how exactly p53 loss promotes PDAC, we are using genetically engineered mouse models combined with single-cell and spatial transcriptomic technologies. In this mouse model, PDAC is driven from adult acinar cells with a tamoxifen-inducible Ptf1aCreER allele by oncogenic Kras (KrasG12D) along with either p53 wild type (p53wt) or p53 deficiency (p53flox). In this model, acinar cells can give rise to PDAC likely through a transdifferentiation process called acinar-to-ductal metaplasia (ADM), which leads to pancreatic intraepithelial neoplasias (PanINs) and then PDAC. The initial cell fate transition, ADM, can be activated by growth factors, inflammation, and injury. We have conducted single-cell and spatial transcriptomics to compare early stages of tumor development in the presence and absence of p53, and we will present our latest analyses. Providing insight into the early events of PDAC will lead to new approaches for improving clinical intervention in human PDAC. Citation Format: Kathryn J. Hanson, Allegra C. Minor, Brittany M. Flowers, Alyssa M. Kaiser, Nicholas Hughes, Hannes Vogel, Le Cong, Laura D. Attardi. The initiation and progression of pancreatic ductal adenocarcinoma through a p53 lens [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr C056.

Design and FPGA implementation of a hyperchaotic conservative circuit with initial offset-boosting and transient transition behavior based on memcapacitor

A charge-controlled memcapacitive conservative chaotic circuit with trigonometric function terms is constructed in this paper. By analyzing the characteristics of the infinite equilibrium point and the divergence of the system, it is proved that the system is conservative. Under the influence of system parameters, hyperchaotic and chaotic characteristics can be switched to each other. With the increase of parameters and initial values, the Lyapunov exponent is also greatly improved. In addition, the transient chaos phenomenon accompanied by the internal crisis is also found, which leads to the sudden change of the orbit state of the attractor, and different types of coexisting attractors in different regions of the basins are also found. Through further analysis of the phase diagram, bifurcation diagram and time-domain waveform, it is found that there are three initial offset-boosting behaviors with different characteristics in the system. Finally, the spectral entropy (SE) algorithm is used to compare the memcapacitive circuit complexity under different initial conditions and system parameters. We find that the SE complexity distribution map is consistent with the Lyapunov exponent trajectory, which further reflects the influence of system parameters and initial conditions on the dynamic characteristics of the system. On the platform of Cyclone IV E series, the FPGA main chip of EP4CE10F17C8N is used to complete the hardware implementation of the system. The FPGA implementation results are consistent with numerical simulation, and verify the realistic feasibility of the memcapacitive conservative chaotic circuit in practical application.

Comprehensive high resolution study of the [formula omitted]SiH[formula omitted][formula omitted] tetradecad stretching bands: Appearance and applications of the isotopic substitution effect in molecules of spherical symmetry

A set of new relations between different spectroscopic parameters of the high symmetry XY4 spherical top molecules is derived on the basis of the general isotopic substitution theory, and a comprehensive high accurate analysis of the five stretching bands (the bands ν1+ν3(F2), 2ν3(F2), 2ν3(E), 2ν3(A1), and 2ν1(A1); the three latter ones are forbidden in absorption) of the tetradecad of the SiH4 molecule is made. The high resolution spectra of MSiH4(M=28,29,30) in their natural abundance were recorded with a Bruker IFS125 HR Fourier transform infrared spectrometer at the Technische Universität Braunschweig, Germany with an optical resolution of 0.003 cm−1 and theoretically analyzed (in this case, for the first time both for all five bands of the 29SiH4 and 30SiH4 species, and for 2ν3(E), 2ν1(A1) bands of the 28SiH4 one). The number of 2713 transitions of the 28SiH4 species (which is more than fourteen times higher compared to analogous studies carried out earlier) belonging to all five ro-vibrational bands of the tetradecad (which are 272, 1897, 15, 369, and 160 transitions of the ν1+ν3(F2), 2ν1(A1), 2ν3(A1), 2ν3(F2), and 2ν3(E) bands) were assigned with the values of quantum number Jmin/Jmax = 5/22, 1/24, 14/20, 4/24, and 6/23, respectively. The analysis of the obtained experimental data was made on the basis of the Hamiltonian model which takes into account all effects and resonance interactions which are possible in such molecular system. The weighted fit of the 2713 transitions led to a set of 40 rotational, centrifugal distortion, tetrahedral splitting, and resonance interaction parameters which reproduce the initial experimental data with an accuracy of drms=4.11×10−4 cm−1. An analogous analysis was made for the two other isotopologues, 29SiH4 and 30SiH4, of silane. In this case, the initial values of the most important spectroscopic parameters of both species were theoretically estimated on the basis of results of the isotopic substitution theory. As the result of the analysis, two sets of the 12 spectroscopic parameters were obtained from the weighted fits for the 29SiH4 and 30SiH4 molecules which reproduce the 461 and 375 initial ro-vibrational transitions with the drms of 3.91×10−4 and 4.9710−4 cm−1.

Teaching Style Preferences and Online Teaching Practices of Optometry Teachers During COVID-19: A Preliminary Study.

Although research on teaching style preferences is available in the literature, there is limited information on the preferences of optometry teachers. The Coronavirus disease 2019 pandemic has impacted educational practices in all sectors. This study focuses on the teaching style preferences and online teaching practices of optometry teachers during the COVID-19 pandemic. The study used a case study research design and a self-administered online questionnaire and follow-up semi-structured interview for data collection. The Grasha-Riechmann teaching style inventory was used to explore the teaching style preferences (Expert, Formal Authority, Demonstrator, Facilitator and Delegator). Quantitative and qualitative data were analyzed using descriptive statistics and thematic content analysis respectively. The optometry teachers were aged between 29 and 51 years (median = 45 years) and had between 3 and 25 years of teaching experience (median = 5 years). All teachers scored high in the Expert teaching style and most had scores categorized as high for the Delegator, Facilitator and Formal Authority teaching styles. The teachers reported that the initial adaptation to online teaching was difficult and challenging as they were not prepared for the rapid transition to online learning. They used various resources and materials but felt that student participation and engagement was lower in online teaching. Teachers noted that more time was needed to prepare materials for online teaching than for face-to-face teaching. Optometry teachers adopted a multidimensional approach preferring the different teaching styles to varying degrees. Teachers noted challenges with the initial transition and adaptation to online teaching and used a combination of resources to support student learning.

Effects of Ni doping on structural, magnetic and catalytic properties of copper ferrite

The aim of this work was to obtain information about the influence of small quantities of Ni2+ ion on the structural and magnetic properties of the tetragonally distorted of Cu1−xNixFe2O4 series (with x = 0.00, 0.05, 0.1, and 0.15 respectively). The tested ferrite system was synthesized by combustion of citrate–nitrate precursors. The synchrotron X-ray diffraction measurements determined the phase transition temperatures (tetragonal → cubic) of all samples. The change of structures under the influence of temperature shows a phase transition in the range of 390 – 400 °C for x = 0.00, 330 – 370 °C for x = 0.05, 210 – 330 °C for x = 0.1 and 140 – 210 °C for x = 0.15, respectively. The initial phase transition temperature decreases linearly with the decreasing c/a ratio of the crystallographic lattice parameters for the Cu1−xNixFe2O4 oxides. Hysteresis measurements were made to determine the saturation magnetization (MS) and coercive field (µ0Hc) of the samples. The values of magnetic moments at room temperature determined from magnetization measurements are very similar to those obtained from theoretical x-ray diffraction calculations. Magnetic moment values per formula unit are estimated to range from 1.16 μB to 1.5 μB. It was found that the catalytic activity of N2O decomposition of samples increases with increasing nickel content.

Modeling fatigue-assisted pitting in pipeline steel with PCA-XFEM

We present a localized corrosion and cracking damage mechanism (initiation of the pit, propagation of the pit, pit-to-crack transition, and stable cracking) in a pipeline steel under the application of fatigue loading by using sequential coupling of Probabilistic Cellular Automata (PCA) and eXtended Finite Element Method (XFEM). PCA is utilized for describing the localized corrosion damage mechanism. XFEM is used to simulate arbitrary inhomogeneities (cracks, voids, and soft/hard material interfaces (inclusions)) with the help of Level Set Methods (LSM). In the XFEM, the standard finite element is enriched by additional degrees of freedom by invoking the notion of the partition of unity, which alleviates the burden of mesh conformity to the internal boundaries and avoids re-meshing. LSM is used to locate the voids and material interfaces and track the crack propagation location. A localized strain criterion initiates cracks from the pit surface when the pit reaches a critical strain value.The coupling of PCA and XFEM demonstrates good agreement with experimental data regarding stress-assisted pitting corrosion and pit-induced fatigue cracking in the pipeline steel. The study also investigates the effects of boundaries, and initial pit size on fatigue crack initiation and growth. Boundary effects significantly influence crack initiation life and growth behavior, highlighting the importance of considering both defect characteristics and boundary conditions in assessing fatigue performance and structural integrity. Various initial pit sizes and geometric features further affect crack initiation location and transition time. Furthermore, the PCA-XFEM model effectively captures crack behavior in both short and long crack regimes, demonstrating good agreement with experimental data for a selected pit width of 140μm. By incorporating crack driving parameters derived from experiments, the model accurately predicts crack propagation, further enhancing its reliability and predictive capabilities in assessing fatigue crack behavior. Overall, this approach provides valuable insights for predicting the service life and integrity of pipelines subjected to similar loading conditions, thus aiding in designing and maintaining these critical infrastructure components.

First principles study on band gap modulation of TiO2 (112) surface for enhancing optical properties

Anatase TiO2 is widely used in solar photocatalysis. However, the optical properties are limited by its ability to capture visible light and its poor activity. In order to obtain ideal material properties, GGA + U method based on density functional theory is used to study the electronic structure and optical properties of anatase phase TiO2 and its (112) surface and Cr and Co-doped TiO2 (112) surface. The results show that the transition metal Cr-doped system is more stable than the Co-doped system. The four systems exhibit semiconducting properties. The indirect band gap value of intrinsic TiO2 is 3.245 eV, and the impurity bands appear in the spin-up energy bands after Cr, Co doping. The impurity states of the doped system spin split, which transforms the non-magnetic semiconductor into a semiconductor with net magnetic moments of 2 μB and 3 μB, respectively. In addition, the Cr, Co-doped systems show excellent optical properties, and the absorption coefficients are red-shifted in the range of (0–3 eV) with higher optical absorptivities. Through the investigation, it is evident that doping results in different degree of band gap change. As the conduction band moves towards the lower energy level, an impurity band is generated near the Fermi level. The presence of the impurity band fundamentally alters the initial transition mode of the electron, making the transition require less energy, thus enabling enhanced optical properties. The doping system enhances the lepton threshold of electrons and light absorption by changing the mode of inter-band leaps and decreasing the reflectivity, making them candidates in the field of optoelectronics and photocatalysis.

Unlocking the advantages of differential pricing: A two‐period model integrating consumer identifiable information and advertising effort

To explore the potential benefits of differentiated pricing compared to uniform pricing within supply chain networks, we constructed a two‐period dynamic pricing model for products in this research. In our scenario, the manufacturer produces the original product during the initial period and introduces a new‐generation product in the subsequent period. Simultaneously, the retailer handles the original product during the initial period and transitions to selling the new‐generation product boosted by advertising efforts in the following period. Our analysis of the proposed models yielded three primary insights. First, the adoption of a differentiated pricing strategy may not universally favor supply chain participants. Second, the implementation of a differentiated pricing approach does not necessarily equate to higher wholesale and retail prices in each period. Finally, to optimize overall profits and attain mutually beneficial outcomes, it is imperative for supply chain stakeholder to share decision‐making information. Furthermore, we offer managerial recommendations based on these findings.

Cycloaliphatic epoxy-functionalized polydimethylsiloxanes for comprehensive modifications of epoxy thermosets

Polydimethylsiloxane (PDMS) are known as a class of efficient modifiers for epoxy thermosets, but the simultaneous improvement in thermal stability, thermomechanical and mechanical properties remain a challenge. Herein, we report a cycloaliphatic epoxy-functionalized polydimethylsiloxane (PDMS-CE) with a designed epoxy value for comprehensive modifications of diglycidyl ether of bisphenol A (DGEBA)/methylhexahydrophthalic anhydride (MeHHPA) thermosets. Compared to neat epoxy thermoset, the 4 wt% PDMS-CE modified epoxy thermoset showed a 79 %, 120 % and 503 % increase in flexural strength, impact strength and fracture toughness, respectively, as well as a slight increase in the initial thermal decomposition temperature (Td5%) and glass transition temperature (Tg), and a desirable decrease in the dielectric constant and water absorption rate. This comprehensive modification performance was caused by the combined effects of crosslinking density improvement, rigid cycloaliphatic structure, as well as the flexible PDMS chains.

Experimental Study on Combustion Modes and Oscillations in a Cavity-Based Scramjet Combustor

This study conducted experiments to investigate flame behaviors in a cavity-based scramjet combustor operating under Mach 2.92 supersonic inflow. Pressure measurements and flame chemiluminescence observations were combined to study the initial flame formation and combustion mode transitions. In addition, flame luminosity standard deviation and fast Fourier transform power spectral density (PSD) were post-processed to assess the impact of equivalence ratio and aft wall height on combustion modes as well as oscillations. It is indicated that increasing the equivalence ratio leads to a transition from lifted shear-layer mode to ramjet mode. Elevating the cavity aft wall height improves the combustor’s self-ignition capability and promotes the transition from lifted shear-layer mode to ramjet mode as long as flame stabilization is achieved. It is found that increasing the equivalence ratio and aft wall height also results in more intense combustion oscillations; besides, raising the cavity aft wall height could accentuate the predominant frequency of low-frequency oscillations in the combustor. Finally, it is demonstrated that the application of spark plasma effectively suppresses these low-frequency combustion oscillations, which is a promising active control method in the scramjet engine.

PRACTICAL EXPLORATION OF THE PROFESSIONAL DEVELOPMENT OF COLLEGE IDEOLOGICAL AND POLITICAL TEACHERS

This study takes the political, theoretical, and belief requirements of college ideological and political courses as the premise and basis, summarizes the characteristics of the professional development of college ideological and political teachers, and extracts the requirements for the professional development of college ideological and political teachers. Under the guidance of the development stage theory, the professional development of college ideological and political teachers is divided into seven periods, which are the pre-service education period, the initial period, the adaptation and transition period, the competence period, the maturity period, the stable period, and the retirement period. According to the characteristics of each stage, explore the practice mode of professional development of teachers of ideological and political courses, such as implementing school-based training, relying on school-based curriculum development, effectively carrying out action research, actively carrying out teaching reflection, building a community of teacher professional development, and conducting scientific teacher evaluation, etc.

Transition care to adolescent hepatology in a tertiary center for rare adult–child liver disease

AimsThis study analyzed the results of a transition program in a patient population with a rare liver disease of pediatric onset. MethodData were collected on the clinical course of an adolescent population with a rare disease of pediatric onset and enrolled in a transition program between 1994 and 2022. ResultsA total of 238 adolescents (including 34 having undergone a liver transplant on enrolling in the program) were included. Eight patients were lost to follow-up before the first transition consultation and 16 families requested follow-up in an adult hepatology department closer to their home. Overall, 214 initial transition consultations were carried out; 29 patients were subsequently lost to follow-up and 13 switched center. Overall, 15.4 % of the patients enrolled in our program were lost to follow-up. Five adult patients underwent a liver transplantation during this 28-year period. Overall mortality was 3.2 %, graft survival was 91.5 %, and posttransplant survival was 92 %. In total, the current active file represents 183 patients with a median age of 24.3 years (18–51) and a median follow-up period of 5.8 years (6 months to 28 years). ConclusionThe implementation of a transition program to adult medicine for adolescents with a rare liver disease should follow the recommendations but must be adapted in line with local practice conditions. This process requires close collaboration between the pediatric and adult medicine teams based on a mutual desire to constantly improve practices and enhance knowledge.

Europa’s coupled ice–ocean system: Temporal evolution of a pure ice shell

Europa’s icy surface likely overlies an ocean, but the ice thickness is not known. Here we model the temporal growth of a Europan shell of pure ice subject to varying ice–ocean heat fluxes, ice rheologies, and internal heating rates. Both constant and viscosity-dependent internal heating rates are included, yielding similar results for particular viscosities. A growing shell starting from an ice-free initial state transitions from conduction to convection at O(105) to O(107) years, with thicknesses of O(1–10) km. For low ice–ocean heat fluxes and larger viscosities, and in the absence of internal heating of the shell, the time to reach a steady-state thickness exceeds the estimated age of Europa’s surface, whence the shell may still be growing. We conclude by presenting a method for inferring estimates of ice–ocean heat fluxes (modulo uncertainties introduced by internal heating) and vertical ocean velocities from the ice-thickness measurements expected from the upcoming Clipper mission, assuming the shell is in a conductive steady state.

In-depth study of structural, magnetic and XPS behavior of the double perovskite La2-xCex/2Erx/2NiMnO6

Structural, morphological, X-ray photoelectron spectroscopy (XPS) and magnetic details of La2-xCex/2Erx/2NiMnO6 (x = 0.00 and 0.025) prepared by the traditional ceramic method were investigated. X ray-diffraction refinements by Rietveld method indicate that our samples have a monoclinic system with the space group P 21/n No. (14). A small amount of MnNi6O8 impurity was detected in both samples. Morphological analysis reveals that our samples contain grains of different sizes equal to 1.249 µm and 1.260 µm for x = 0.00 and 0.025. Mapping and EDX analysis confirm the existence and homogeneous distribution of elements on the surface of our samples. According to the x-ray photoelectron spectroscopy (XPS) analysis, the presence of a trivalent oxidation state La and RE ions, along with a mixed-valence state of Ni and Mn ions, has been confirmed in the samples. For magnetic analysis, a double transition temperature is detected from the dM/dT variation for the FC curve. The initial transition (T1) occurs at lower temperatures, approximately 105 K and 110 K for x = 0.00 and x = 0.025, respectively. On the other hand, the second transition T2 (Tc) takes place at higher temperatures, around 250 K and 265 K, respectively, for x = 0.00 and x = 0.025. These two magnetic transition temperatures are attributed to distinct spin states of Mn and Ni cations. Thus, the low-temperature transition (T1) can be attributed to a vibronic super-exchange interaction involving trivalent oxidation states, specifically Ni3+–O–Mn3+. The higher temperature transition T2 (Tc) was defined as the Curie temperature when the system undergoes a transition from the ferromagnetic (FM) to the paramagnetic state (PM). The magnetocaloric effect (MCE) exhibits the presence of two prominent peaks. The first one is at low temperature around 80 K. The second is at high temperature around 250 K. A phonemological approach called Landau theory was used to deduce the variation of the magnetic entropy (-ΔSM). Good agreement is obtained between the experimental behavior of (- ΔSM) and that predicted by this theory.

Nucleation Work on Curved Substrates

Nucleation is the initial phase transition process when nuclei of a new phase form within an undercooled or supersaturated parent phase under appropriate conditions. Nucleation most often occurs through a heterogeneous process on active centers on which the probability of nucleus formation is high. In general, the origin of active centers may be difficult to distinguish. In this work, we consider the formation of crystalline nuclei in a melt on various curved substrates. Knowledge of excess free energy plays a key role in understanding the process of formation of clusters and it is not easy to express this quantity in a considered system. Excess free energy is often approximated within the framework of capillarity approximation based on interfacial energy, which depends on interatomic interactions near the interface, as well as the misfit between melts, surface roughness, temperature, composition, etc., near the phase interface. The formation of nuclei requires overcoming a certain energy (nucleation) barrier that is a consequence of balancing the volume and the interfacial free energy. Knowing the nucleation barrier (W) is crucial for understanding this process, as nuclei predetermine the physical properties of a newly formed phase. W is typically expressed as a function of the nucleus radius; however, in nucleation kinetics, one needs to determine (W) as a function of the number of molecules forming the nucleus. We analyze nucleation work on various substrates (flat, convex, and concave) for crystallization from an aluminum melt to show that the formation of nuclei is the most probable on concave substrates. An analytical expression for W can be easily applied to other systems under consideration. We show that under the same conditions, the critical radius of nuclei is identical for various substrate, in contrast with the critical number of molecules forming a nucleus.

Laser powder bed fused 304L steel shot-peened with various ceramic shot sizes: Surface/subsurface characteristics, tensile behavior, and fatigue behavior

Shot peening is an efficient post-processing technique for eliminating surface manufacturing defects, inducing compressive residual stress, and improving the mechanical properties of laser powder bed fused (L-PBFed) metallic materials. With a series of microstructural characterizations, this work comprehensively evaluated the influence of ceramic shot size on the surface characteristics, subsurface characteristics, and mechanical properties, especially fatigue performance, of L-PBF manufactured 304L austenitic stainless steel (SS). The mechanical testing process was in situ observed using an infrared thermal camera, and the tensile-fractured and fatigue-fractured microstructures were systematically examined, aiming to explore the life improvement mechanisms caused by different ceramic shot sizes. The results revealed that when compared to small-sized AZB 100 shots, the large-sized AZB 300 shots could result in higher surface roughness, larger thickness reduction, more apparent surface gradient structure, higher strength, and longer fatigue lifetimes. The strength improvement could be associated with the size reduction of L-PBF induced subsurface defects, the grain refinement at the surface layer, and the α'-martensitic transformation during tensile deformation. The life improvement could be primarily attributed to the subsurface defect strengthening, which resulted in the fatigue crack initiation transition from subsurface defects to surface defects. During the fatigue process, the energy dissipation originating from the core materials dominated the thermal equilibrium temperature, whereas the density of micro-defects (crystalline defects) at the surface layer dominated the crack tip temperature. These findings provide a basic understanding of how to advance the shot peening process for L-PBFed materials.

Biomimetic Cardiac Tissue Models for In Vitro Arrhythmia Studies.

Cardiac arrhythmias are a major cause of cardiovascular mortality worldwide. Many arrhythmias are caused by reentry, a phenomenon where excitation waves circulate in the heart. Optical mapping techniques have revealed the role of reentry in arrhythmia initiation and fibrillation transition, but the underlying biophysical mechanisms are still difficult to investigate in intact hearts. Tissue engineering models of cardiac tissue can mimic the structure and function of native cardiac tissue and enable interactive observation of reentry formation and wave propagation. This review will present various approaches to constructing cardiac tissue models for reentry studies, using the authors' work as examples. The review will highlight the evolution of tissue engineering designs based on different substrates, cell types, and structural parameters. A new approach using polymer materials and cellular reprogramming to create biomimetic cardiac tissues will be introduced. The review will also show how computational modeling of cardiac tissue can complement experimental data and how such models can be applied in the biomimetics of cardiac tissue.