Discontinuities In Structure Research Articles

Compilation of Stress Concentration Factors in the Vicinity of a Geometric Discontinuity in Structures

The analytical method estimates the stress concentration factor (Kt) using theoretical equations, while the numerical approach overcomes the limitations of analytical solutions in dealing with complex geometries. Simulations were conducted to evaluate how variations in hole diameter affect the stress concentration factor, revealing that larger diameters significantly increase the stress concentration factor. The presence of holes induces localized over-stress, compromising structural integrity. The research focuses on circular and elliptical holes under tensile loading, integrating both analytical and numerical techniques. Results validated against analytical solutions pinpoint areas of maximum stress concentration, which are crucial for the design and optimization of perforated structures. This study provides valuable insights for engineers, enhancing understanding of perforated plates' behavior under load, ultimately improving their reliability and safety in various industrial applications. The primary aim is to quantify the SCF, highlighting the risks posed by geometric discontinuities and their potential to lead to plastic deformation or structural failure.

Topography immune-responsive silk films for skin regeneration.

Scar formation and chronic refractory wounds pose a significant threat to public health, with abnormal immune regulation as a key characteristic. However, topography, a crucial factor influencing immune responses, has not been adequately considered in the design of wound dressings. In this study, we constructed a hierarchical structure on silk fibroin (SF) films by combining soft lithography and femtosecond laser ablation, without altering the intrinsic properties of SF. The discontinuity in the hierarchical structure induced a transformation in the morphology of macrophage RAW264.7 cells from round to spindle or pancake-like shapes, leading to phenotypic polarization toward M2 or M1. The timely transition from M1 to M2 polarization and the balance between these states promoted fibroblast L929 cells to express mRNA for FN, coll-I, TGF-β1, and α-SMA. The hierarchical structure of SF films facilitates full-thickness wound repair in vivo by regulating inflammation and promoting neovascularization and collagen deposition. Thus, hierarchical topography presents a promising strategy for the design of immunomodulatory wound dressings.

Identity and Temporal Fragmentation in Borderline Personality Disorder: A Systematic Review.

Borderline Personality Disorder (BPD) is a prevalent psychopathological condition, affecting 0.7-2.7% of the general population. Given the known link between identity formation and the temporal, metacognitive, and narrative processes that contribute to its coherence, the aim of the present systematic review is to synthesize the current literature about the relationship between identity diffusion and lived time in adult patients with BPD. This would enhance knowledge and treatments, leading to a better understanding of the implications of time processes on identity diffusion in BPD. According to PRISMA guidelines, the main databases were consulted, and specific eligibility criteria were applied. The selection leads to the inclusion of 15 articles, investigating through integrated techniques the lived time, memory, self-reported narratives, and metacognition in BPD subjects. A general agreement among researchers was found, confirming greater difficulty for BPD subjects in producing autobiographical stories, logically and temporally integrated, characterized by positive content. Functional and structural alterations were detected to explain narrative incoherence, as well as symptoms such as emotional dysregulation and cognitive biases. The difficulty for BPD subjects in producing a coherent personal narrative has been interpreted as a correlation of anomalies in autobiographical memories and consequently identities, which were equally compromised by the experience of discontinuity in the temporal structure. This would confirm the hypothesis of the temporal fragmentation of the self in BPD. Although some limitations have been encountered, we suggest that the understanding of identity diffusion and lived time in BPD subjects could represent a useful guide for further research.

Research and application of joint-constrained inversion of transient electromagnetic multivariate parameter

Due to the phenomena of stratigraphic inclination, complex structure, and lateral discontinuity of resistivity or layer thickness in most of the coal seams, the traditional one-dimensional transient electromagnetic inversion method has limitations in interpretation accuracy. In addition, two- and three-dimensional inversion and artificial intelligence inversion have problems of large computation and large sample size, respectively, which limit their application in small- and medium-sized engineering exploration. To improve the inversion effect, this study proposes a method of joint-constrained inversion of transient electromagnetic multivariate parameters. This method achieves the joint constraint inversion of the transient electromagnetic multi-parameter by making full use of the geological data and a priori information to construct the initial model and adding the constraints such as the resistivity, the thickness, and the layer interface of each layer in the inversion objective function, and at the same time, taking into account the spatial correlation of the stratigraphic structure between the neighboring measurement points, as well as the transverse and vertical constraints between the measurement points along the direction of the survey line and perpendicular to the survey line. First, a series of typical geoelectric models are established and numerically simulated, and the results are compared with those of the traditional inversion method to verify the applicability and effectiveness of the method. Then, the constrained inversion is carried out on the physical simulation and measured data, and the results are in good agreement with the actual geological conditions. The numerical simulation, physical simulation and measured data inversion results consistently prove that this method can effectively reduce the uncertainty of the inversion at the isolated measuring points, improve the spatial continuity of the formation boundary, and better reflect the actual geoelectric characteristics of the formation.

Magnesium sulphate resistance of fly ash one-part geopolymers: Influence of solid alkali activators on physical, mechanical and chemical performance

The commitment to promoting circular economy and durable construction materials has led to the advocacy for one-part geopolymer (OPG), as an eco-friendly substitute for traditional ordinary Portland cement (OPC). Solid alkali activator is the fundamental component of OPG and significantly influences the sulphate resistance. To identify the types of solid alkali activators best suited for the development of sulphate-resistant OPGs, OPGs activated with Na2SiO3 (M-OPG), Na2SiO3+Na2CO3 (MC-OPG), Na2SiO3+NaOH (MH-OPG) and Na2SiO3+NaAlO2 (MA-OPG) were exposed to 5 % and 10 % of MgSO4 solutions for 28 days. The fine pore structures of MH-OPG and MC-OPG mitigated deterioration from the more concentrated MgSO4 solution, resulting in higher residual compressive strengths after exposure to the 10 % MgSO4 compared to the 5 %. Exposure to the 5 % MgSO4 solution resulted in strength deterioration for M-OPG, MH-OPG and MC-OPG due to the discontinuity of the aluminosilicate structure, as evidenced by the diminished Q4(3Al) sites. Conversely, the MA-OPG exhibited a 24.1 % increase in compressive strength, accompanied by the emergence of sodium magnesium aluminium silicate hydrate ((N,M)-A-S-H) gel. Hence, Na2SiO3+NaAlO2 should be acknowledged as the primary candidate for solid alkali activators in the development of sulphate-resistant OPGs.

Multiscale porosity characterization in additively manufactured polymer nanocomposites using micro-computed tomography

Extrusion-based additive manufacturing (AM) of polymer composites exhibits complex thermally driven phenomena that introduce severe discontinuities in the internal structure across length scales, especially voids or porosity. This study utilizes a high-throughput porosity characterization technique to analyze large datasets from numerous micro-computed tomography (μCT) scans to capture the influence of AM print parameters on the size, shape, and location of porosity across multiple print layers (up to a few cm) on fused granular fabrication (FGF) printers. The materials investigated include nanocomposite formulations based on commercially relevant nylon-12 and polyether ketone ketone (PEKK) materials comprising nano- or micro-sized fillers. The estimated global porosity follows an inverse linear correlation against the bulk density of the printed samples. Increasing the extrusion multiplier (EM) and the nozzle temperature while decreasing the print speeds reduces the global porosity. Outlier analyses (local porosity morphology) show that faster print speeds and higher extrusion rates result in long, slender inter-layer voids, while lower nozzle temperatures lead to large, symmetrical, inter-bead voids (at the bead junction). Lack of active chamber temperature increases inter-layer and intra-bead voids with a two-fold increase in global porosity. Overall, the micro filler-reinforced composites exhibit higher global porosity than nanofiller-reinforced composites, which is attributed to the increased mismatch in the thermal expansion coefficient between the filler and the polymers used in the study.

Ground penetrating radar observations of the contact between the western delta and the crater floor of Jezero crater, Mars.

The delta deposits in Jezero crater contain sedimentary records of potentially habitable conditions on Mars. NASA's Perseverance rover is exploring the Jezero western delta with a suite of instruments that include the RIMFAX ground penetrating radar, which provides continuous subsurface images that probe up to 20 meters below the rover. As Perseverance traversed across the contact between the Jezero crater floor and the delta, RIMFAX detected a distinct discontinuity in the subsurface layer structure. Below the contact boundary are older crater floor units exhibiting discontinuous inclined layering. Above the contact boundary are younger basal delta units exhibiting regular horizontal layering. At one location, there is a clear unconformity between the crater floor and delta layers, which implies that the crater floor experienced a period of erosion before the deposition of the overlying delta strata. The regularity and horizontality of the basal delta sediments observed in the radar cross sections indicate that they were deposited in a low-energy lake environment.

Police education reform in Iceland: examining the legitimating principles, contradictions, and tensions in policy discourse

ABSTRACT In recent decades, in many countries, police education has shifted from vocational training schools run by the police to universities. In Iceland, in 2016, basic police education was reformed, the National Police Academy was closed, and a new university programme was created. In this article, we analyse the discourse in two reports from 2014 and 2015 and two legal texts from 2016 leading up to this education reform. A six-step approach to discourse analysis was utilised. Our main research questions were as follows: What characterises the discourse of police education reform in Icelandic policy documents? What are the discourse’s main legitimating principles, tensions, and contradictions? We identified two contrasting legitimating principles in the discourse: the validation of police competence through a university diploma versus policing as a unique public-sector profession. There is a discontinuity in both social structures and practices, leading to a new approach to knowledge development via research and university education. This shift has produced uncertainty, as well as tensions that can occur when traditional vocational training is transformed into university programmes. These findings could have implications for other occupations seeking professional status with a strong tradition of control over their own basic training and knowledge bases.

Dynamic modelling and parametric analysis of a bolted joint rotor-bearing system considering stick-slip behavior at mating interface

Bolted joint structure is widely utilized in the aeroengine compress rotor systems with convenience in assembly and maintenance. Due to the inherent structure discontinuity and stick-slip behavior at the mating interface, stiffness softening and frictional energy dissipation would be generated at the mating interface, resulting in complex vibration features of the rotor system. In this work, to describe the stick-slip behavior at the mating interface of the rotor system, an Iwan-based model is introduced to describe the contact state of asperities at the multi-scale level. The corresponding model identification method is proposed based on the partial hysteresis curve of the bolted joint. After that, a dynamic model of the bolted joint rotor system is established, and its dynamic response is obtained using the Runge–Kutta method. The effect of preload and friction coefficient on the nonlinear vibration of the bolted joint rotor is evaluated in detail based on the dynamic model. The result indicates that the stiffness softening would lead to the critical speed decreasing and aggravating the vibration response of the rotor system, while the frictional energy dissipation would restrain the response amplitude and induce the self-excited vibration within the super-critical speed range. The higher preload or friction coefficient has little effect on the motion state of the rotor system within the sub-critical speed range and makes system vibration stable between the 1st- and 2nd-order critical speed while unstable at the super-critical speed range. This research helps understand the vibration features of bolted joint rotor systems under the condition of stick-slip behaviors at the mating interface.

Exploring T.S. Eliot’s The Waste Land as a Pre-postmodern Text

Despite being a groundbreaking literary work of Modernism, T.S. Eliot’s poem The Waste Land heralds the new era of Postmodernism that officially begins almost two decades after its publication. Although Eliot is one of the best representatives of modernist poets, his major work The Waste Land foreshadows some postmodern techniques and concepts. A seminal modernist poem of 1922, it can also be read as a postmodernist poem in the making. The present paper analyses some postmodern elements in The Waste Land and finds it a great epic of pre postmodernist thoughts. Its intertextuality, fragmentation, discontinuity in narrative structure, and deconstruction of meaning put The Waste Land closer to postmodernism.

Accelerated multi-hillshade hierarchic clustering for automatic lineament extraction

The lineaments are linear features reflecting mountain ridges or discontinuities in the geological structure. Lineament extraction is not an easy problem. Recently, an automatic approach based on multi-hillshade hierarchic clustering (MHHC) has been developed; the approach is based on line extraction from a raster image. An essential part of this approach is spatial line segment clustering, a powerful but relatively slow tool. This paper presents a modification of MHHC, which solves the spatial line segment clustering as a facility location problem. The proposed modification is faster than MHHC while not changing the method’s core.

Stream Fanning and Bifurcations: Observable Signatures of Resonances in Stellar Stream Morphology

Recent observations have revealed a trove of unexpected morphological features in many of the Milky Way’s stellar streams. Explanations for such features include time-dependent deformations of the Galactic gravitational potential, local disruptions induced by dark matter substructure, and special configurations of the streams’ progenitors. In this paper, we study how these morphologies can also arise in certain static, nonspherical gravitational potentials that host a subset of resonantly trapped orbit families. The transitions, or separatrices, between these orbit families mark abrupt discontinuities in the orbital structure of the potential. We develop a novel numerical approach for measuring the libration frequencies of resonant and near-resonant orbits and apply it to study the evolution of stellar streams on these orbits. We reveal two distinct morphological features that arise in streams on near-resonant orbits: fans, which come about due to a large spread in the libration frequencies near a separatrix, and bifurcations, which arise when a separatrix splits the orbital distribution of the stellar stream between two (or more) distinct orbit families. We demonstrate that these effects can arise in some Milky Way streams for certain choices of the dark matter halo potential and discuss how this might be used to probe and constrain the global shape of the Milky Way’s gravitational potential.

Alginate/guacamole edible films as moisture barrier layers in multicomponent foods

AbstractIn multicomponent foods having both moist and dry components (e.g., pizzas and tacos), moisture migration between components causes undesirable texture changes (e.g., loss of crispiness of the dry component). In this study, different proportions of alginate (film matrix), guacamole (hydrophobic component with sensory appeal), and glycerol (plasticizer) were combined to form edible films to be used as a moisture barrier between moist and dry components of multicomponent foods. Alginate was the component that most contributed to increase the film strength and to reduce its water vapor permeability (WVP). Guacamole, due to the presence of avocado lipids, enhanced the film hydrophobicity, although not having decreased the WVP (as expected), since it promoted discontinuities in the alginate structure. The film with the lowest WVP (containing an alginate/guacamole/glycerol dry mass ratio of 25/60/15) was inserted between nachos and tomato sauce, being able to reduce the crispiness loss of nachos during a 50‐min storage.

Estimation of Durability of HC-550 Floor Slabs Based on Electrochemical Tests of Corrosion Rate of Reinforcement Strings in Concrete

The consequences of the loss of the load-bearing capacity due to the corrosion of prestressing steel can be much more dangerous than in the case of reinforced concrete structures, since failure can occur quite rapidly and without warning. A very important issue, therefore, is to determine the factors affecting the durability of prestressed structures exposed to aggressive agents, especially chloride ions. The aim of this study was to verify the protective properties of concrete of prefabricated HC-type prestressed concrete slabs in order to evaluate the possibility of their application in the ceilings of multilevel garages. In this paper, the corrosion rate of rebar steel in HC-550 floor slabs at a width of 1200 mm was estimated with nondestructive electrochemical methods: linear polarization and impedance spectroscopy. The general and mechanical properties of concrete prepared according to a formula in a laboratory and analogous concrete cut directly from the analyzed floor slabs were also studied. The porosity of concrete from these slabs was determined using X-ray-computed tomography for pore-related characterization. The values of the diffusion coefficient of chloride ions determined in previous works and the previously proposed model for the overexposure of the durability of floor slabs in chloride-containing environments were used to determine the durability of these slabs. Based on the empirical correlations adopted from the literature presenting the relationship of durability/adhesion over time and the corrosion parameters studied, a safe service life was determined at the nominal class of concrete equal to Δtcor.red = 30.48 years. In addition, in the case of discontinuities in the concrete structure, there may be a dangerous reduction in the time of corrosion initiation and a subsequent reduction in service life due to the loss of the adhesion of strut strands for up to 10.68 years of service life.

Voids Development in Metals: Numerical Modelling.

The article is a continuation of two previous review papers on the fracture mechanism of structural metals through the nucleation, growth and coalescence of voids. In the present paper, the literature on the numerical modelling of void nucleation and development has been reviewed. The scope of the work does not include porous material models and their numerical implementation. As part of the discussion on void initiation, nucleation around second phase particles and nucleation as an effect of the discontinuity of the crystal structure were discussed separately. The basic void cell models, finite element method (FEM) models of periodically distributed particles/voids and models based on the results of the observations of the actual microstructure of materials have been characterised. Basic issues related to the application of the cohesive approach in void nucleation modelling have been considered. A separate issue is the characteristics of atomistic simulations and peridynamic modelling, which have been developed in recent years. Numerical approaches to modelling the growth and coalescence of voids are described, with particular emphasis on the influence of the stress state and strain localisation. Basic conclusions from the simulation are presented, pointing to the contribution of FEM modelling to the understanding of microstructural phenomena leading to ductile fracture.

Performance analysis of gallium nitride-based DH-HEMT with polarization-graded AlGaN back-barrier layer

In this paper, polarization-graded AlGaN back-barrier nanolayer has been introduced to improve the DC and RF parameters of gallium nitride-based high electron mobility transistors (HEMT). To explore the characteristics, both graded and non-graded double heterojunction high electron mobility transistor (DH-HEMT) structures are optimized using SILVACO-ATLAS physical simulator. Enhanced DC and RF parameters have been observed in the optimized graded DH-HEMT. In this paper, we have also studied the development of the quantum wells at the AlGaN/GaN interfaces due to the conduction band discontinuity in both structures.

Seismic Performance of Frame Structure with Hysteretic Intermediate Discontinuity

The introduction of an intermediate discontinuity in frame structures is commonly named inter-storey isolation. Inter-storey isolation is an effective technique for the seismic protection of new or existing frame structures. The devices that are used to perform the discontinuity, mainly of the structural stiffness, are placed at a higher storey level of the structure and not at the base level. In the latter years, this technique has gained increasing interest because, especially for existing buildings, it is cheaper and technically easier to implement than base isolation. In this paper, the attention is focused on the effects on a frame structure of an intermediate elasto-plastic discontinuity that can be described by a Bouc-Wen model. The frame structure with the intermediate discontinuity is modelled with a 3-DOF reduced model. Its dynamical behaviour is investigated by considering both harmonic and seismic external excitation. The results are summarized in gain maps aimed at finding the parameters that optimize the seismic behaviour of the structure.

Experimental Investigation on Shear Capacity of Steel-Fiber-Reinforced High-Strength Concrete Corbels.

As short cantilever members, corbels are mainly used to transfer eccentric loads to columns. Because of the discontinuity of load and geometric structure, corbels cannot be analyzed and designed using the method based on beam theory. Nine steel-fiber-reinforced high-strength concrete (SFRHSC) corbels were tested. The width of the corbels was 200 mm, the cross-section height of the corbel column was 450 mm, and the cantilever end height was 200 mm. The shear span/depth ratios considered were 0.2, 0.3, and 0.4; the longitudinal reinforcement ratios were 0.55%, 0.75%, and 0.98%; the stirrup reinforcement ratios were 0.39%, 0.52%, and 0.785%; and the steel fiber volume ratios were 0, 0.75%, and 1.5%. According to the test results, this paper discusses the failure process and failure mode of corbel specimens with a small shear span/depth ratio and analyzes the effects of variables such as shear span/depth ratio, longitudinal reinforcement ratio, stirrup reinforcement ratio, and steel fiber volume content on the shear capacity of corbels. The shear capacity of corbels is significantly affected by the shear span/depth ratio, followed by the longitudinal reinforcement ratio and the stirrup reinforcement ratio. Moreover, it is shown that steel fibers have little impact on the failure mode and ultimate load of corbels, but can enhance the crack resistance of corbels. In addition, the bearing capacities of these corbels were calculated by Chinese code GB 50010-2010 and further compared with ACI 318-19 code, EN 1992-1-1:2004 code, and CSA A23.3-19 code, which adopt the strut-and-tie model. The results indicate that the calculation results by the empirical formula in the Chinese code are close to the corresponding test results, while the calculation method based on the strut-and-tie model of a clear mechanical concept yields conservative results, and hence the related parameter values must be further modified.

Characterization of Cassava Starch Extruded Sheets Incorporated with Tucumã Oil Microparticles

The application of biopolymers and feasible technologies to obtain sheets is crucial for the large-scale production of food packages and for reducing plastic pollution. Additionally, the inclusion of additives in sheets can affect and improve their properties. This work aimed to incorporate tucumã oil (TO) and TO microparticles produced by spray drying (SD), spray chilling (SC), and their combination (SDC) into extruded cassava starch sheets and to evaluate the effect of such addition on their physical, optical, and mechanical properties. Gum Arabic and vegetable fat were used as wall materials for SD and SC/SDC, respectively. The sheets enriched with tucumã oil (FO) and the microparticles produced by SD, SC and SDC (FSD, FSC, and FSDC, respectively) presented yellow color (hue angle around 90°) and higher opacity (11.6–25.3%) when compared to the control (6.3%). All sheets showed high thickness (1.3–1.8 mm), and the additives reduced the water solubility of the materials (from 27.11% in the control to 24.67–25.54% in enriched samples). The presence of large SDC particles, as evidenced by Scanning Electron Microscopy (SEM), caused discontinuity of the sheet structure and decreased mechanical strength of the FSDC. One may conclude that potential active packages were obtained by extrusion of cassava starch sheets added with pure and encapsulated TO.

Compact acoustic amplifiers based on non-adiabatic compression of sound in metamaterial waveguides

Inspired by the optical non-adiabatic wave propagation effect in plasmonic waveguides, we explore the acoustic non-adiabatic wave compression effect in acoustic metamaterial waveguides, and demonstrate its potential for the development of compact metamaterial devices with significant sound amplification capability. In particular, our numerical and experimental results have shown that there exists combined effects of structure discontinuity and thermal viscous dissipations in the metamaterial waveguides, which is essential to reduce the size of metamaterial device and optimize its field enhancement capability. Our work provides a new way to design high-performance and compact metamaterial devices that could be practically used in automotive ultrasonic radars, robot sonar systems, structural health monitoring and medical instrumentation and imaging applications.