Formation Of Boundaries Research Articles

Racist dogs and classist rats?

In cities across the world, animals reflect, reproduce and transform urban inequalities – yet their role in mediating social hierarchies remains undertheorized. Urban scholars have begun to highlight the importance of infrastructures and technologies in configuring access to essential goods and services. While this research provides key insights into how non-human entities mediate unequal relations, it has largely overlooked how certain animals – „political animals“ – also co-produce inequalities. This article focuses on two critical urban domains, security and public health, that are often characterized by stark inequalities, and takes the role of key animals within these domains – dogs and rats, respectively – as a new analytical entry-point. Security dogs are socialized to identify threatening individuals on the basis of classed and raced markers. Rats thrive in upscale neighborhoods with historical architecture and abundant green space – yet the public health risks and the stigma associated with these rodents may disproportionately affect low-income residents. Drawing on research on security dogs in Kingston, Jamaica and rats in Amsterdam, this talk discusses the role of animals in the formation of sociospatial boundaries, and the distribution of resources and risks across urban spaces and populations. Focusing on the interactions these two types of „political animals“ have with both humans and infrastructure, it sets out a research agenda for studying how animals’ everyday encounters with their cultural and material environments combine to result in (in-)equitable social outcomes.

Physical mechanism of the intermittent plastic flow at extremely low temperatures

The physical mechanism of the intermittent plastic flow (IPF) of austenitic steels at extremely low temperatures is explained in the context of microstructure evolution and 3D deformation arising in the area of the shear band. The microstructure change is identified by X-ray diffraction with the use of synchrotron radiation as well as electron backscatter diffraction (EBSD). This complete, global and local, approach reveals the intensive formation of twin boundaries which perform two functions. They become a part of the macroscopic shear band, but also constitute barriers piling up dislocations. Thus, their overcoming results in a stress drop as in the case of breaking the Lomer-Cottrell locks. The investigations show that the rapid displacement is blocked by the intensively produced martensite α’. The main features of the uncovered microstructural evolution are captured in the 3D reconstruction of the shear band obtained with the use of profilometer. Moreover, the effect of the thermodynamic instability is taken into account when assessing the conditions of the IPF. Finally, new kinetics of the IPF is developed. It comprises two functions: B reflecting the surface density of the dislocation pile-ups on the internal lattice barriers, and G corresponding to the surface density of twin boundaries. The breakthrough of the work consists in the discovery of multi-scale mechanism of the IPF, including participation of twin boundaries and the Lomer-Cottrell barriers.

TiC-induced nanoscale Cu-rich re-precipitation mechanism under welding thermal cycles and its effect on the strength-toughness of heat affected zones

In order to solve the softening problem of welding heat affected zone (HAZ) for Cu-bearing steel caused by the dissolution of Cu-rich particles, TiC was utilized to induce the Cu-rich re-precipitation. With the peak temperature increased from 780 °C (ICHAZ) to 950 °C (FGHAZ), the size of 9R–Cu increases from 4 nm to 5 nm, accompanied with the increment of volume fraction from 0.6% to 1.0%. Phase field simulations indicate that TiC repels Cu atoms into γ-Fe matrix and promotes the formation of Cu-rich clusters. Then, Cu-rich clusters provide more nucleation sites for Cu-rich particles, which contributed to the re-precipitation of refined 9R–Cu. Due to the disappearance of coarse grain boundary Cu-rich particles and formation of fresh lath bainite, re-precipitated Cu-rich particles provided precipitation strengthening value of 237 MPa and 298 MPa without decreasing the low temperature toughness for ICHAZ and FGHAZ. The yield strength and absorbed energy at −40 °C of HAZs exceed 1000 MPa and 120J, respectively.

Cu/Zn bimetallic catalysts prepared by facial potential steps electrodeposition favoring Zn deposition and grain boundary formation for efficient CO2ER to ethylene

Electro-reduction of CO2 (CO2ER) is a promising way to reduce atmospheric CO2 meanwhile gaining high-value-added products (e.g. ethylene). Introducing zinc, a kind of cheap, non-hazardous metal into copper, can perform tandem catalytic functions to overcome the disadvantage of pure Cu. However, due to the quite different theoretical reduction potentials of Cu2+ and Zn2+, Cu/Zn bimetallic catalysts are difficult to be synthesized using the electrochemical method. Here, a facial Potential Steps electrodeposition (PSE) method was proposed to prepare Cu/Zn bimetal catalyst supported on a gas diffusion layer (CuZn/GDE), during which, a lower voltage only suitable for Cu’s deposition was firstly applied, and then a higher voltage was imposed. Worthy mentioned, during the first step, Zn2+ could also transfer to the cathode from the bulk solution and then be embedded by the deposited Cu, forming a capsule-analogous micro-reaction environment composed of highly electron-conductive Cu and enriched Zn2+, thus decreasing the over-potential of Zn’s deposition, further promoting the reduction of Zn & the formation of Cu/Zn grain boundary and the stabilization of Cu(I) in the second step. The optimized CuZn/GDE could achieve a high faradaic efficiency to ethylene (40.2 %) at −1.36 V vs RHE in H-cell. The DFT calculations showed that the *CO formation energy at Cu/Zn and Cu(0)/Cu(I) was lower than at pure Cu and that the formation of *COCOH at Cu(0)/Cu(I) was more thermodynamically favorable than at pure Cu. This work supplies a facial and effective strategy to synthesize copper-based bimetallic catalysts for CO2ER, which could decrease the over-potential of the metal with high deposition potential, and meanwhile form grain boundary, in favor of generation of C2 products.

Offcut Substrate-Induced Defect Trapping at Step Edges.

We report step edge-induced localized defects suppressing subsequent antiphase boundary formation in the bulk structure of a trilayer oxide heterostructure. The heterostructure encompasses a layer of La0.66Sr0.34MnO3 sandwiched between a superconducting La1.84Sr0.16CuO4 bottom layer and an insulating La2CuO4 top layer. The combination of a minor a-axis mismatch (0.11 Å) and a pronounced c-axis mismatch (2.73 Å) at the step edges leads to the emergence of localized defects exclusively forming at the step edge. Employing atomically resolved electron energy-loss spectroscopy maps, we discern the electronic state of those structures in the second La0.66Sr0.34MnO3 unit cell near the step edge. In particular, a reduction in the pre-edge region of the O-K edge indicates the formation of oxygen vacancies induced by the strained step edge. This study underscores our capability to control defects at the nanoscale.

Mechanisms of grain boundary α precipitation in the metastable β-titanium Ti-5Al-5Mo-5V-3Cr

In this study, we investigated the early nucleation and growth of grain boundary α during the aging heat treatment of Ti-5553. Through a correlative approach using scanning electron microscopy, electron backscatter diffraction, transmission Kikuchi diffraction, transmission electron microscopy, and atom probe tomography, high-angle β-grain boundaries were investigated in detail to understand the evolution of the precipitation of grain boundary α through nucleation and subsequent growth. It is found that at grain boundaries there is a pronounced nucleation of α precipitates with similar orientations. Growth of these similarly orientated α precipitates, in the later stages, leads to their agglomeration and the formation of grain boundary α. This investigation provides insights into the formation of grain boundary α in its early stages of nucleation and growth.

Extrinsic hydrophobicity-controlled silver nanoparticles as efficient and stable catalysts for CO2 electrolysis.

To realize economically feasible electrochemical CO2 conversion, achieving a high partial current density for value-added products is particularly vital. However, acceleration of the hydrogen evolution reaction due to cathode flooding in a high-current-density region makes this challenging. Herein, we find that partially ligand-derived Ag nanoparticles (Ag-NPs) could prevent electrolyte flooding while maintaining catalytic activity for CO2 electroreduction. This results in a high Faradaic efficiency for CO (>90%) and high partial current density (298.39 mA cm‒2), even under harsh stability test conditions (3.4 V). The suppressed splitting/detachment of Ag particles, due to the lipid ligand, enhance the uniform hydrophobicity retention of the Ag-NP electrode at high cathodic overpotentials and prevent flooding and current fluctuations. The mass transfer of gaseous CO2 is maintained in the catalytic region of several hundred nanometers, with the smooth formation of a triple phase boundary, which facilitate the occurrence of CO2RR instead of HER. We analyze catalyst degradation and cathode flooding during CO2 electrolysis through identical-location transmission electron microscopy and operando synchrotron-based X-ray computed tomography. This study develops an efficient strategy for designing active and durable electrocatalysts for CO2 electrolysis.

Anomalous twin boundary formation in magnesium alloys by rapid solidification

The aim of this work is to investigate the formation of an anomalously high fraction of twin boundaries (TBs) during laser directed energy deposition (DED) of a Mg-3Al-1 Zn (wt.%) alloy. With that goal, single tracks are deposited using different combinations of scan speed and powder feed rate. The melt pool dimensions are related to the DED parameters. Irrespective of the processing conditions, the resulting microstructures are always formed by fine grains with a very weak texture. However, some DED parameter combinations give rise to a fraction of TBs that is significantly higher than that corresponding to a random texture. These TBs are characterized by an irregular morphology and by the presence of segregated atoms, solute clusters, and nanoparticles. Additionally, the lattice in the vicinity of the TBs is highly distorted and contains a high population of stacking faults. All these characteristics set them apart from conventional tensile TBs, which exhibit a large degree of coherency and limited segregation. Rapid solidification is thus presented here as a novel avenue to design TBs with unique properties in Mg alloys. This work paves the way for future studies on grain boundary design via additive manufacturing methods, a field that is still in its infancy.

Investigation of effect of post weld heat treatment on microhardness and microstructure of auto TIG welded stabilized SA213 TP347H weldments

Investigation explores the weldability of Niobium stabilized TP347H austenitic stainless steel tubes through the application of optimized welding parameters using Auto TIG welding. This research investigates the influence of post weld heat treatment conditions on microhardness, microstructures, sensitization due to Cr23C6 precipitation, presence of Niobium carbides and formation of twin boundaries in the weldment. Extended post weld heat treatment duration resulted in notable decline in microhardness from 280 to 180 VHN within initial 5-h of soaking. Nevertheless, further prolongation of soaking time (10–15 h) exhibited subsequent rise in microhardness levels to 200 VHN in base, weld and heat affected zone. Increase in hardness is attributed to the emergence of annealing twins in base metal and the precipitation of Niobium carbides within weld and heat affected zone, confirmed by advanced analytical scanning electron microscope. Energy dispersive spectrum line mapping reveals presence of Cr23C6 precipitation following 1-h soak at 720 °C. Subsequent prolongation of soaking time (5-h) demonstrates desensitization in the base metal. Additionally, cooling rate of 300 °C/hr during post weld heat treatment reduces required time for microstructure homogenization, resulting in increased hardness compared to 100 °C/hr rate in the weldment. However, beyond a 5-h soaking time, the cooling rate has a negligible impact on microhardness. Ultimate Tensile Stress of 674.82 and 665.28 N/mm2 for TP347H was achieved against the minimum requirement of 515 N/mm2 as per American Society of Mechanical Engineers Section IX standard.

Delineating the Ultra-Low Misorientation between the Dislocation Cellular Structures in Additively Manufactured 316L Stainless Steel.

Sub-micro dislocation cellular structures formed during rapid solidification break the strength-ductility trade-off in laser powder bed fusion (LPBF)-processed 316L stainless steel through high-density dislocations and segregated elements or precipitates at the cellular boundaries. The high-density dislocation entangled at the cellular boundary accommodates solidification strains among the cellular structures and cooling stresses through elastoplastic deformation. Columnar grains with cellular structures typically form along the direction of thermal flux. However, the ultra-low misorientations between the adjacent cellular structures and their interactions with the cellular boundary formation remain unclear. In this study, we revealed the ultra-low misorientations between the cellular structures in LPBF-processed 316L stainless steel using conventional electron backscatter diffraction (EBSD), transmission Kikuchi diffraction (TKD), and transmission electron microscopy (TEM). The conventional EBSD and TKD analysis results could provide misorientation angles smaller than 2°, while the resolution mainly depends on the specimen quality and scanning step size, and so on. A TEM technique with higher spatial resolution provides accurate information between adjacent dislocation cells with misorientation angles smaller than 1°. This study presents evidence that the TEM method is the better and more precise analytical method for the misorientation measurement of the cellular structures and provides insights into measuring the small misorientation angles between adjacent dislocation cells and nanograins in nanostructured metals and alloys with ultrafine-grained microstructures.

First-Principles Understanding on the Formation of Inversion Domain Boundaries of Wurtzite AlN, AlScN, and GaN

First-Principles Understanding on the Formation of Inversion Domain Boundaries of Wurtzite AlN, AlScN, and GaN

Predicting yield stress in a nano-precipitate strengthened austenitic steel by integrating multi length-scale simulations and experiments

A promising high-strength Fe – 17.7Mn – 4.7Cr – 0.48C – 10Ni – 5Al – 4Cu wt.% Austenitic steel was solutionized, then aged for 3 or 10 h at 580 °C producing a pronounced precipitation hardening response primarily due to the formation of nanoscale NiAl precipitates. Density functional theory (DFT), molecular dynamics (MD), and discrete dislocation dynamics (DDD) calculations were combined with microstructural data from atom-probe tomography (APT), informing theoretical strengthening models to predict yield strength at different stages of precipitation as a function of NiAl size, volume fraction, and composition. These yield strength predictions were compared with experimental microhardness measurements of the various ageing conditions, including the peak microhardness of 490 HV, which corresponds to an estimated alloy yield strength of 1200 MPa. Comparing MD calculations with theoretical models showed that anti-phase boundary (APB) formation was the predominant barrier to dislocation motion posed by the NiAl precipitates. Using single dislocation particle strengthening models with NiAl APB energies calculated from DFT, good agreement was observed between DDD calculations and the 10 h peak-aged experimental measurements, while agreement with the 3 h experimental measurements required reducing the NiAl APB energy. These results demonstrate the utility of the undertaken approach integrating simulations and experiments across multiple length-scales, particularly the presented coarse-grained DDD simulation method towards modeling materials strengthened by very fine precipitates. The results further suggest that the observed NiAl precipitates may adopt an alternate crystal structure early in their formation.

Interdependent Formation of Symbolic and Regulatory Boundaries: The Discursive Contestation Around the Home-Sharing Category

The formation of boundaries between established and emergent categories is a complex social process. Therein, our understanding of how symbolic boundaries translate into regulatory boundaries is underdeveloped. Extant research either treats laws and regulations for categories as given or assumes a seamless translation of a symbolic into a regulatory boundary. This sidelines that market participants actively contest and shape boundaries between categories. To address this lacuna, we open the black box of how symbolic boundaries are translated into regulatory boundaries. We adopt a discursive perspective and conduct a longitudinal study of the contestation around the categories of home sharing and short-term rental in Europe. Our analysis shows how symbolic and regulatory boundaries are formed in a causal sequential process, driven by shifts in the field positioning of market actors and in the discursive accounts they mobilize. We develop a theoretical model of the discursive foundation of category boundary formation. At the heart of our theorization are discursive accounts and how shifting coalitions of market participants mobilize them to shape the evolving symbolic and regulatory boundaries between an emergent and an established category. We contribute to category research by unearthing the interdependent formation of symbolic and regulatory boundaries and the role of discursive accounts in these processes.

SAFB restricts contact domain boundaries associated with L1 chimeric transcription

Long interspersed element-1 (LINE-1 or L1) comprises 17% of the human genome, continuously generates genetic variations, and causes disease in certain cases. However, the regulation and function of L1 remain poorly understood. Here, we uncover that L1 can enrich RNA polymerase IIs (RNA Pol IIs), express L1 chimeric transcripts, and create contact domain boundaries in human cells. This impact of L1 is restricted by a nuclear matrix protein scaffold attachment factor B (SAFB) that recognizes transcriptionally active L1s by binding L1 transcripts to inhibit RNA Pol II enrichment. Acute inhibition of RNA Pol II transcription abolishes the domain boundaries associated with L1 chimeric transcripts, indicating a transcription-dependent mechanism. Deleting L1 impairs domain boundary formation, and L1 insertions during evolution have introduced species-specific domain boundaries. Our data show that L1 can create RNA Pol II-enriched regions that alter genome organization and that SAFB regulates L1 and RNA Pol II activity to preserve gene regulation.

Architecting strength: Innovative microstructural design of Aluminum/Alumina Nanocomposites via cold-welded flaky-shaped particles and pressure-assisted sintering

Aluminum/alumina (Al/ Al2O3) nanocomposites with three different microstructural architectures were prepared using flake powder metallurgy, which involves the conversion of spherical Al powder into nanoflakes by ball milling, the introduction of Al2O3 by natural oxidation, the control of the powder microstructure by cold welding, and then powder by densification, sintering, and extrusion. The experimental results showed that the shape of the Al matrix grains and the distribution of native Al2O3, the so-called Al/Al2O3 architectures, could be precisely controlled by BM. The nanolaminate architecture, in which the Al2O3 nanoplatelets were aligned along the boundaries of lamellar or elongated grains, exhibited a more balanced combination of tensile strength and ductility than the random architecture with non-uniformly distributed Al2O3 nanoplatelets within equiaxed grains. This improvement can be attributed to the combined effect of higher Al2O3 strengthening efficiency and better work hardening ability. The research results suggest that the presence of Al2O3 nanoplatelets at high-angle grain boundaries significantly hinders the main mechanism of subgrain rotation for the formation of new boundaries. Moreover, the simulation accurately predicts the higher degree of grain faceting in finer-grained samples, which is consistent with the experimental data indicating more pronounced hexagonal grain shapes. Consequently, flake powder metallurgy offers a promising approach for the production of strong and ductile Al-matrix composites through the design of their microstructural architecture.

Manipulating nanostructure during wire arc additive manufacturing defeats hydrogen embrittlement

Wire arc additive manufacturing (WAAM) leads to a unique nano/microstructure. The combination of multiscale experimental and numerical analyses firstly shows that the intrinsic heat treatment during WAAM leads to an unusual depletion of Mg near the grain boundaries. During the WAAM process, a high dislocation density leads to formation of sub-grains and high-angle grain boundaries (HAGBs). It is assumed that the uniformly distributed micropores formed during the WAAM are strong hydrogen traps. The reduction in Mg content at the HAGBs, an increase in total length of HAGBs and hydrogen trapping by micropores help to defeat intergranular hydrogen embrittlement by WAAM.

Microstructure evolution and mechanical properties of refractory high-entropy alloy nitride film

The (TiZrNbMo)Nx refractory high-entropy alloys (RHEAs) nitride films were fabricated using reactive magnetron sputtering by modifying the N2 flow rate ratio in the mixed N2 + Ar atmosphere. The incorporation of the N element induced a phase transition in the (TiZrNbMo)Nx films from body-centered cubic (BCC) to face-centered cubic (FCC) structure, accompanied by increasing in the amorphous phase. With the introduction of N2, the hardness of (TiZrNbMo)Nx films firstly increased significantly to 25.2 GPa when the N2 flow rate ratio was at 50 % and then decreased slightly to 18.5 GPa when the N2 flow rate ratio was at 75 %. Theoretical analysis shows that the doping of N element enhances the solid strengthening effect, with the formation of nitride phases and grain boundary (GB) strengthening effect significantly contributing to the enhanced hardness. Furthermore, the addition of N element can also inhibit grain rotation and GB sliding during deformation. This work provides a new insight into understanding the structure and properties of refractory high-entropy alloy films.

Personal boundaries: definition, role, and impact on mental health

This article attempts to generalize and systematize existing knowledge in psychology about the phenomenon of personal boundaries and their influence on an individual's psychological well-being. The first section of the article analyzes the concept of personal boundaries, their functions, and types. It explains that personal boundaries are defined as internal and external spaces that separate the individual from the surrounding world and others. Various types of boundaries are considered, including physical, emotional, mental, and spiritual boundaries. The second section of the article discusses the peculiarities of forming personal boundaries and typical disruptions in their functioning. It is noted that the formation of healthy boundaries occurs throughout life and depends on interactions with parents, the surrounding environment, and individuality. Typical boundary violations are also considered, such as lack of awareness, stress, fear of refusal, and others. The third section examines the guarantee of forming healthy personal boundaries. The role of assertiveness in maintaining healthy boundaries and effective interaction with the surrounding world is analyzed. It is explained that assertive behavior helps maintain a balance between one's own needs and the interests of others, contributing to the construction of stable and constructive relationships. The conclusions emphasize the importance of understanding and awareness of personal boundaries for maintaining mental health and improving the quality of life. They highlight the significance of developing assertiveness and other key skills to support healthy boundaries and build harmonious relationships with the world. This scientific article is an important source for those interested in personality psychology, interaction with the environment, and the development of mental health. It offers a deep analysis of the basic concepts of personal boundaries and provides practical recommendations for their preservation and support.

Combinatorial and high-throughput investigation of growth nanotwin formation

This study examines the synthesis of growth nanotwins in CuNi alloys using combinatorial and high-throughput experimental techniques. 338 unique CuNi samples were synthesized via co-sputtering to create a material library encompassing composition, hardness, phase, and crystallographic data. The material library data in conjunction with scanning transmission electron microscopy was used to evaluate growth twinning over a wide compositional range (Cu – 6.8 to 58.8 at% Ni). A direct correlation between measured twin boundary spacings and the stacking fault energies underscored limitations of the current growth twin model caused by an underestimation of the free energy penalty for forming non-twinned grains. To address this, a refined model was developed to accurately capture the variation in twin boundary spacing and formation across all compositions. This model paves the way for high-throughput investigations into nanotwin synthesis in various alloy systems.

Unveiling the Synergistic Role of Frustrated Lewis Pairs in Carbon-Encapsulated Ni/NiOx Photothermal Cocatalyst for Enhanced Photocatalytic Hydrogen Production.

The development of high-density and closely spaced frustrated Lewis pairs (FLPs) is crucial for enhancing catalyst activity and accelerating reaction rates. However, constructing efficient FLPs by breaking classical Lewis bonds poses a significant challenge. Here, this work has made a pivotal discovery regarding the Jahn-Teller effect during the formation of grain boundaries in carbon-encapsulated Ni/NiOx (Ni/NiOx @C). This effect facilitates the formation of high-density O (VO ) and Ni (VNi ) vacancy sites with different charge polarities, specifically FLP-VO -C basic sites and FLP-VNi -C acidic sites. The synergistic interaction between FLP-VO -C and FLP-VNi -C sites not only reduces energy barriers for water adsorption and splitting, but also induces a strong photothermal effect. This mutually reinforcing effect contributes to the exceptional performance of Ni/NiOx @C as a cocatalyst in photothermal-assisted photocatalytic hydrogen production. Notably, the Ni/NiOx @C/g-C3 N4 (NOCC) composite photocatalyst exhibits remarkable hydrogen production activity with a rate of 10.7 mmol g-1 h-1 , surpassing that of the Pt cocatalyst by 1.76 times. Moreover, the NOCC achieves an impressive apparent quantum yield of 40.78% at a wavelength of 380nm. This work paves the way for designing novel defect-state multiphase cocatalysts with high-density and adjacent FLP sites, which hold promise for enhancing various catalytic reactions.