Boundary Spacing Research Articles

Rethinking our chemical legacy and reclaiming our planet

Rethinking our chemical legacy and reclaiming our planet

Computational design synthesis for Fabrication-Aware assembly problems using building objects with dimensional variations

State-of-the-art computational design approaches for designing the assembly of a structure often rely on high-precision building objects, which can be difficult and costly to fabricate. To consider a wider range of construction materials and fabrication processes, e.g. low-cost 3D printing and brick making, this research introduces a novel computational design method for fabrication-aware assembly problems using existing building components with dimensional variations. Given a finite set of building objects, this study develops a statistical preprocessing approach and a modified pattern search with an efficient integer linear programming method to generate the assembly of a target structure, such that it is statically stable and optimized for geometric smoothness and space utilization. In two case studies, the proposed algorithm exhibits significantly better boundary fitting and space utilization compared with a genetic algorithm and a standard pattern search method and lower computational cost compared with a genetic algorithm.

Artificial Intelligence Capability and Organizational Creativity: The Role of Knowledge Sharing and Organizational Cohesion.

The rapid development of artificial intelligence (AI) has brought many opportunities and challenges to organization. Some studies have shown that AI can improve organizational creativity. However, the existing research lacks an effective transformation path. This paper makes an innovative approach from the perspective of knowledge sharing, establishes an integration model of artificial intelligence capability, knowledge sharing and organizational creativity. Based on 189 questionnaire data, we use multi-level regression analysis and bootstrap method to analyze the influence mechanism. The results show that artificial intelligence has a positive effect on knowledge sharing, knowledge sharing has a positive effect on organizational creativity, knowledge sharing mediates the relationship between artificial intelligence and organizational creativity, and organizational cohesion has a positive moderating effect on the relationship between artificial intelligence and knowledge sharing. The results supplement the existing research on the relationship between artificial intelligence capability and organizational creativity, expand the theoretical boundary and application space from the perspective of knowledge sharing at the organizational level, and provide reference for organizations to improve creativity.

Effect of Twin Boundary Density on Mechanical Behavior of Al0.1CoCrFeNi High-Entropy Alloy by Molecular Dynamics Simulation

Molecular dynamics simulation method was used to study the influence of co-lattice twin boundary (TB) spacing on the deformation behavior of Al0.1CoCrFeNi high-entropy alloy single crystal under uniaxial tension. Studies have shown that there is a “critical distance” between the twin boundaries, and the sensitivity of the two sides to the change of the twin spacing is different, and the influence of the evolution of the deformation mechanism of the different twin spacing is analyzed from the number of defects and the evolution of the dislocation density. The results show that as the distance between twins decreases, the deformation mechanism gradually transforms from dislocation slip accompanied by defects, such as stacking faults and secondary twins, to a deformation mode of amorphous phase transition. The research aims to provide guidance and reference for the design of high-performance high-entropy alloys.

Influence of volume and aspect ratio of liquid bridges on capillary breakup rheometry

Capillary thinning of liquid bridges is routinely used for extensional rheology of Newtonian and complex fluids. Although it is expected that the volume and aspect ratio of a liquid bridge significantly influence its dynamics, the role played by these parameters in rheological characterization has not been previously studied. We perform numerical simulations of Newtonian as well as viscoelastic liquid bridges with the one-dimensional slender-filament approximation of Eggers and Dupont [“Drop formation in a one-dimensional approximation of the Navier–Stokes equation,” J. Fluid Mech. 262, 205–221 (1994)] and Ardekani et al. [“Dynamics of bead formation, filament thinning and breakup in weakly viscoelastic jets,” J. Fluid Mech. 665, 46–56 (2010)]. Sample volume and bridge aspect ratio control two phenomena that can adversely impact rheological characterization: the tendency to form satellite drops at the necking plane and the slowing down of capillary thinning due to the proximity (in parameter space) of the liquid-bridge stability boundary. The optimal range of these parameter values to avoid drop formation and slowdown is discussed.

Boundary quotient C*‐algebras of semigroups

We study two classes of operator algebras associated with a unital subsemigroup P $P$ of a discrete group G $G$ : one related to universal structures and one related to co-universal structures. First we provide connections between universal C*-algebras that arise variously from isometric representations of P $P$ that reflect the space J $\mathcal {J}$ of constructible right ideals, from associated Fell bundles, and from induced partial actions. This includes connections of appropriate quotients with the strong covariance relations in the sense of Sehnem. We then pass to the reduced representation C λ ∗ ( P ) $\mathrm{C}^*_\lambda (P)$ , and we consider the boundary quotient ∂ C λ ∗ ( P ) $\partial \mathrm{C}^*_\lambda (P)$ related to the minimal boundary space. We show that ∂ C λ ∗ ( P ) $\partial \mathrm{C}^*_\lambda (P)$ is co-universal in two different classes: (a) with respect to the equivariant constructible isometric representations of P $P$ ; and (b) with respect to the equivariant C*-covers of the reduced non-selfadjoint semigroup algebra A ( P ) $\mathcal {A}(P)$ . If P $P$ is an Ore semigroup, or if G $G$ acts topologically freely on the minimal boundary space, then ∂ C λ ∗ ( P ) $\partial \mathrm{C}^*_\lambda (P)$ coincides with the usual C*-envelope C env ∗ ( A ( P ) ) $\mathrm{C}^*_{\text{env}}(\mathcal {A}(P))$ in the sense of Arveson. This covers total orders, finite type and right-angled Artin monoids, the Thompson monoid, multiplicative semigroups of non-zero algebraic integers, and the a x + b $ax+b$ -semigroups over integral domains that are not a field. In particular, we show that P $P$ is an Ore semigroup if and only if there exists a canonical ∗ $*$ -isomorphism from ∂ C λ ∗ ( P ) $\partial \mathrm{C}^*_\lambda (P)$ , or from C env ∗ ( A ( P ) ) $\mathrm{C}^*_{\text{env}}(\mathcal {A}(P))$ , onto C λ ∗ ( G ) $\mathrm{C}^*_\lambda (G)$ . If any of the above holds, then A ( P ) $\mathcal {A}(P)$ is shown to be hyperrigid.

Design of pure aluminum laminates with heterostructures for extraordinary strength-ductility synergy

• Pure aluminum laminates with various heterostructures were engineered via extrusion, rolling and annealing. • The designed laminates exhibited an excellent strength-ductility synergy. • The evolution of GNDs was observed using in-situ tension. • The strain gradient across the hetero-interface was revealed using DIC technique. • Hetero-deformation induced (HDI) strengthening and hardening contributed to the superior mechanical properties. Heterogeneous metals and alloys are a new class of materials with superior mechanical properties. In this paper, we engineered sandwich-structured pure aluminum laminates composed of middle coarse-grained layer and outer fine-grained layer via extrusion, rolling and annealing. By controlling the post-annealing regimes, a larger degree of microstructure heterogeneities such as boundary spacing, misorientation and texture across the hetero-interface were obtained, which resulted in obvious mechanical differences. Tensile tests indicated that the 300 °C/30 min annealed laminates enabled a relatively high tensile ductility while simultaneously retaining a high strength, which was better than prediction by the rule-of-mixture. To explain the reasons behind it, the evolution of geometrically necessary dislocations and strain gradient at the hetero-interface zone were detected using in-situ tension and microscopic digital image correlation technique. It was found that with the increasing applied strain, a significant strain gradient was developed near the interface, which was accommodated by geometrically necessary dislocations, thereby contributing to higher hetero-deformation induced (HDI) strengthening and hardening.

A Study on the Architectural Plan for Revitalization of Gap in Boundary Space - focusing on Ilshin Textile Factory and Jeonnam Textile Factory Site Utilization Plan

A Study on the Architectural Plan for Revitalization of Gap in Boundary Space - focusing on Ilshin Textile Factory and Jeonnam Textile Factory Site Utilization Plan

Outside the Safe Operating Space of the Planetary Boundary for Novel Entities.

We submit that the safe operating space of the planetary boundary of novel entities is exceeded since annual production and releases are increasing at a pace that outstrips the global capacity for assessment and monitoring. The novel entities boundary in the planetary boundaries framework refers to entities that are novel in a geological sense and that could have large-scale impacts that threaten the integrity of Earth system processes. We review the scientific literature relevant to quantifying the boundary for novel entities and highlight plastic pollution as a particular aspect of high concern. An impact pathway from production of novel entities to impacts on Earth system processes is presented. We define and apply three criteria for assessment of the suitability of control variables for the boundary: feasibility, relevance, and comprehensiveness. We propose several complementary control variables to capture the complexity of this boundary, while acknowledging major data limitations. We conclude that humanity is currently operating outside the planetary boundary based on the weight-of-evidence for several of these control variables. The increasing rate of production and releases of larger volumes and higher numbers of novel entities with diverse risk potentials exceed societies’ ability to conduct safety related assessments and monitoring. We recommend taking urgent action to reduce the harm associated with exceeding the boundary by reducing the production and releases of novel entities, noting that even so, the persistence of many novel entities and/or their associated effects will continue to pose a threat.

Structural transformation and strain localization at twin boundaries in Al0.4CoCrFeNi high-entropy alloy

Surface nanotribological properties and subsurface damage of Al0.4CoCrFeNi high-entropy alloy during the nano-scratching processes are investigated using molecular dynamics. The results show that the surface wear characteristics and scratching-caused surface damage significantly depend on the crystallographic orientation, spacing and inclination angle of the twin boundary. For the variation of crystallographic orientation, the largest friction coefficient belongs to the crystallographic orientation [001], indicating that the movement of the indenter in this substrate is most restricted. The microstructure evolution reveals the formation of Lomer-Cottrell and Hirth dislocation locks because of the distinctness of angle between various slip systems. Both the Hall–Petch and inverse Hall–Petch relationships are observed for the difference of twin boundary spacing, and the maximum indentation force is achieved with a tilt angle of 0° resulting from the various interactions among the dislocations and twin boundaries. The microstructure evolution and the atomic flow are greatly dependent on the spacing and the inclination angle of twin boundary, where the twin boundary migration is the significant factor. Furthermore, the surface morphology is distinct between workpieces due to the elastic recovery at the surface, nucleation and slipping of dislocation, which implies that the wear volume depends on the material microstructure.

Tracking and Monitoring of the Alignment System Used for Nuclear Physics Experiments

The ELI-NP (Extreme Light Intensity—Nuclear Physics) project, developed at the Horia Hulubei National Institute for RD in Physics and Nuclear Engineering (IFIN-HH), has included one component dedicated to the study of interactions between brilliant gamma-ray and matter, with applications in nuclear physics and the science of materials. The paper is focused on the interaction chamber, an important part of the facility which hosts the experiment’s samples. The interaction chamber is endowed with a mobile sample support (holder), which automatically tracks the γ-ray beam. The γ-ray radiation source presents a slight variation of the direction of the emitted radiation in time. The built system ensures the permanent collimation between the γ-ray beam and the sample that is being investigated. This is done with two electric motors, which have a symmetrical movement with respect to the center of a rectangle. The specific measures taken by the design and implementation that permit to reach performances of tracking system are emphasized in the paper. The methodology considers the relative displacement between the detectors with which the laboratory is equipped and the absolute position in space of the sample boundary. The control of this motion is designed to respect the symmetry of the system. Both facets of the project (hardware and software) are detailed, emphasizing the way in which the designers ensured compliance with the system of real-time operation conditions of the tracking and monitoring system.

Age-hardening mechanisms of heterogeneous-nanostructured SUS316LN stainless steel fabricated by heavy cold rolling

A stable SUS316LN austenitic stainless steel was heavily cold-rolled to 92% in reduction to have complicated heterogeneous nanostructure composed of “eye”-shaped twin domains, shear bands and conventional low-angle lamellae. The average boundary spacings in the twin domains and the low-angle lamellae were approximately 25 nm and 40 nm, respectively. The average width of the shear bands was about 40 nm. While the tensile strength along transverse direction was notably high to be 1.9 GPa, it was further raised up to 2.2 GPa by peak aging at 748 K. Nevertheless, any hardening mechanisms as spinodal decomposition, formation of G.P. zone, clustering, etc. could not be detected. The 3D-atom probe tomography analyses revealed segregation of the solute elements of Mo, Si and so on at twin and low-angle lamellar boundaries. A finite element calculation using the multiscale crystal plasticity simulation system indicated rise of strength due to impediment of dislocation motion by the grain-boundary segregation. The combined mechanisms of nano-lamellar structure and grain-boundary segregation, therefore, caused extremely high strengthening.

Multi-phase field simulation of competitive grain growth for directional solidification

The multi-phase field model of grain competitive growth during directional solidification of alloy is established. Solving multi-phase field models for thin interface layer thickness conditions, the grain boundary evolution and grain elimination during the competitive growth of SCN-0.24-wt% camphor model alloy bi-crystals are investigated. The effects of different crystal orientations and pulling velocities on grain boundary microstructure evolution are quantitatively analyzed. The obtained results are shown below. In the competitive growth of convergent bi-crystals, when favorably oriented dendrites are in the same direction as the heat flow and the pulling speed is too large, the orientation angle of the bi-crystal from small to large size is the normal elimination phenomenon of the favorably oriented dendrite, blocking the unfavorably oriented dendrite, and the grain boundary is along the growth direction of the favorably oriented dendrite. When the pulling speed becomes small, the grain boundary shows the anomalous elimination phenomenon of the unfavorably oriented dendrite, eliminating the favorably oriented dendrite. In the process of competitive growth of divergent bi-crystal, when the growth direction of favorably oriented dendrites is the same as the heat flow direction and the orientation angle of unfavorably oriented grains is small, the frequency of new spindles of favorably oriented grains is significantly higher than that of unfavorably oriented grains, and as the orientation angle of unfavorably oriented dendrites becomes larger, the unfavorably oriented grains are more likely to have stable secondary dendritic arms, which in turn develop new primary dendritic arms to occupy the liquid phase grain boundary space, but the grain boundary direction is still parallel to favorably oriented dendrites. In addition, the tertiary dendritic arms on the developed secondary dendritic arms may also be blocked by the surrounding lateral branches from further developing into nascent main axes, this blocking of the tertiary dendritic arms has a random nature, which can have aninfluence on the generation of nascent primary main axes in the grain boundaries.

Effects of orientation and twin boundary spacing on the mechanical behaviour of γ-TiAl alloy

ABSTRACT γ-TiAl alloy is a promising structural material applied in the aerospace and automotive industries. However, its mechanical behaviour is still not well characterised at the atomic scale. In this work, the roles of orientation and twin boundary (TB) spacing on the mechanical properties and deformation behaviours of γ-TiAl alloy are investigated by molecular dynamics simulation with embedded-atom potential under shear loading. The simulation results reveal that the shear modulus is the largest when shearing along [100] and smallest along orientation. The yield stress is the highest of [100] and lowest of orientation. The deformation mechanism and the strain hardening effect differ with orientations. Moreover, it is found that TB migration perpendicular to the loading direction is good at strengthening γ-TiAl alloy. Specifically, 3.79 nm is the critical spacing corresponding to the maximum stress, average peak stress, stress relaxation and the largest strain hardening factor. The shear modulus and yield stress are independent of the TB spacing. The study shows that 3.32 nm is the critical spacing for the TB to annihilate. More importantly, TB migration is the main deformation mechanism at first. Then, it is controlled by the interaction between dislocation-dislocation and dislocation-TB at different TB spacings.

Leveraging accelerator spaces to foster knowledge communities

Knowledge communities are critical for spurring innovation. For knowledge communities to develop and thrive, appropriate choices must be made around their geographic locations, as well as their physical and digital infrastructure. This paper explores the role of the materiality of boundary spaces, specifically geography and physical/digital infrastructure, in knowledge communities using startup accelerators as an empirical context through which to examine their development and structure. Based on a multi-case study of seventeen accelerators in the San Francisco Bay Area, we shed light on how to leverage boundary space design to foster knowledge communities. Using the construct of knowledge communities, we identify three accelerator archetypes – (1) knowledge spoke hubs, (2) knowledge centers, and (3) knowledge networks – and describe the distinct roles that boundary space design plays in each. The discovery of these archetypes and the associated boundary space design considerations inform a discussion about the implications for both the knowledge community and startup accelerator literature.

Microstructure and Texture Evolution during Severe Plastic Deformation at Cryogenic Temperatures in an Al-0.1Mg Alloy

The deformation structures formed in an Al-0.1Mg single-phase aluminium alloy have been studied during plane strain compression (PSC) down to liquid nitrogen temperature, following prior equal channel angular extrusion (ECAE) to a strain of ten. Under constant deformation conditions a steady state was approached irrespective of the temperature, where the rate of grain refinement stagnated and a minimum grain size was reached which could not be further reduced. A 98% reduction at 77 K (−196 °C) only transformed the ECAE processed submicron grain structure into a microstructure with thin ribbon grains, where a nanoscale high angle boundary (HAB) spacing was only approached in the sheet normal direction. It is shown that the minimum grain size achievable in severe deformation processing is controlled by a balance between the rate of compression of the HAB structure and dynamic recovery. The required boundary migration rate to maintain a constant boundary spacing is found far higher than can be justified from conventional diffusion-controlled grain growth and at low temperatures, a constant boundary spacing can only be maintained by invoking an athermal mechanism and is considered to be dominated by the operation of grain boundary dislocations.

Effects of dislocation boundary spacings and stored energy on boundary migration during recrystallization: A phase-field analysis

The local migration of recrystallization boundaries into spatially varying deformation fields which are typical for metals deformed to low and high strains is investigated using quantitative phase-field simulations. It is found that the average migration velocities as well as the local velocities of the recrystallization boundaries critically depend on the spacing between planar geometrically necessary boundaries (GNBs) which are present in the deformation microstructure. Also the morphology of the deformation field reflecting low and high strain deformation cases strongly affect the migrating boundary during recrystallization. Additional simulations were performed as a function of the two critical parameters- stored energy and GNB spacing - independently. Two regimes are found suggesting that these two parameters are closely linked. Previous experimental results are interpreted based on these novel simulation results.

Mechanical Properties of Rolled Copper Foils in Cryogenic and Room‐Temperature Environments

The mechanical properties of high‐purity asymmetric rolled copper foils under cryogenic‐temperature and room‐temperature conditions are studied. The experimental results show that the ultimate tensile stress of the foils increases to a certain value (rolling reduction ratio ≈80%) and then decreases with a decrease in thickness when the tensile tests are carried out in the room‐temperature environment, which monotonically increases with the decrease in the foil thickness when the tensile tests are carried out in a cryogenic environment. The effect on the tensile strength of the copper foil is related to the intrinsic microstructural parameters, such as the dislocation density, grain boundary spacing, and dislocation source. The tensile test results at room and cryogenic temperatures reveal that the elongation decreases with an increase in the rolling reduction ratio. Interestingly, the copper foils of the tensile test at the cryogenic temperature exhibit better elongation than that at the room temperature.

Formation of Nanolaminated Structure with Enhanced Thermal Stability in Copper

Nanolaminated structure with an average boundary spacing of 67 nm has been fabricated in copper by high-rate shear deformation at ambient temperature. The nanolaminated structure with an increased fraction of low angle grain boundaries exhibits a high microhardness of 2.1 GPa. The structure coarsening temperature is 180 K higher than that of its equiaxial nanograined counterpart. Formation of nanolaminated structure provides an alternative way to relax grain boundaries and to stabilize nanostructured metals with medium to low stacking faults energies besides activation of partial dislocations.

Multi‐Stage Hydrothermal Veins in Layered Gabbro of the Oman Ophiolite: Implications for Focused Fluid Circulation in the Lower Oceanic Crust

AbstractAn outcrop in the layered gabbro section from the Wadi Wariyah of the Oman ophiolite has been investigated to provide new insights into the hydrothermal activities that cover a large temperature range in the lower crust at fast‐spreading mid‐ocean ridges. Our observations reveal a complex veining system composed of gabbroic dikes, hydrous mineral (amphibole, epidote, and prehnite) veins and associated alteration, which strongly overprinted the layered gabbros shortly after the solidification of the gabbroic cumulates. The general strike of the veins is roughly perpendicular to the magmatic foliation of the layered gabbro. Mineral‐based geothermometry indicates a wide temperature range (ca. 1,000−250°C) of hydrothermal activities, spanning from hydrous suprasolidus stage (VHT) through amphibolite facies (HT) and epidote‐amphibolite facies (MT) down to the prehnite‐pumpellyite facies (LT), which induced significant differences in selective element depletion and enrichment as well as in exchange of Sr and O isotopes. A key observation is the omnipresence of relics from a previous temperature stage in a given hydrothermal paragenesis formed at lower temperatures, implying that the same pathways were used for hydrothermal veining in a broad temperature interval spanning about 750°C. Our observations support a model that focused fluid circulations, in the form of combined microcracking (grain boundary spacing) and macrocracking (veining), developed shortly subsequent to the complete solidification of the layered gabbros, which may have facilitated effective cooling for magma crystallization in the lower crust.