Complex Path Research Articles

Mechanical behavior and strength criterion of frozen silty clay under complex stress paths

Frozen soil masses under various geologic conditions are usually in complex stress states and may carry complex loads with different stress paths. Thus, a comprehensive understanding of the mechanical behaviors of frozen soil under different stress paths is crucial to guide frozen soil engineering and develop the frozen soil mechanics. In this work, triaxial compressive tests under 32 stress paths were conducted on frozen silty clay, taking both global and local strain measurements. The test stress paths were composed of nine initial confining pressures and 14 stress increment direction angles, whose influences on the mechanical behavior were investigated. The coupling effects between them on the strength and deformation characteristics were revealed: the lower the initial confining pressure was, the stronger the effects of the stress increment direction angle on the strength and deformation were, and the larger the stress increment direction angle was, the stronger the effects of the initial confining pressure on the strength and deformation were. This coupling indicated that the influence of the stress path on the stress–strain response might depend on the change of density during loading: the denser the specimen was, the less the anisotropic it was. The uniqueness of the strain increment directions for a certain stress state reached through different stress paths was found, when assuming the direction of the strain rate coincided with that of the stress. An asymmetric failure function in the meridian plane was proposed, and then a three-dimensional strength criterion was constructed by combining the deviatoric-plane failure function of the unified strength criterion. The validity of the proposed criterion was examined by using stress-path test results of three types of frozen geomaterials in the literature.

Geometric rules for the annihilation dynamics of step lines on fracture fronts.

The roughness of a fracture surface records a crack's complex path through a material and can affect the resultant frictional or fluid transport properties of the broken medium. For brittle fractures, some of the most prominent surface features are long, step-like discontinuities called step lines. In heterogeneous materials, the mean crack surface roughness created by these step lines is well captured by a simple, one-dimensional ballistic annihilation model, which assumes the creation of these steps is a random processes with a single probability that depends on the heterogeneity of the material, and that their destruction occurs via pairwise interactions. Here, through an exhaustive study of experimentally generated crack surfaces in brittle hydrogels, we examine step interactions and show that interaction outcomes depend on the geometry of the incoming steps. The rules that govern step interactions can be categorized into three unique classes and are fully described, providing a complete framework for predicting fracture roughness.

The Way Toward Growth: A Time-series Factor Decomposition of Socioeconomic Impulses and Urbanization Trends in a Pre-crisis European Region

The present study investigates long-term urbanization and suburbanization trends in a divided region of Mediterranean Europe (Attica, Greece). A time series (1965–2008) dynamic factor analysis of 14 indicators that reflect different aspects of metropolitan growth, allowed estimating the impact of economic expansion and social change on the local development path characteristic of the study area. To quantify the spatio-temporal propagation of socioeconomic impulses to local development, Attica was partitioned in two spatial domains, the ‘Greater Athens’ area (hereafter the ‘core’ district) and the rest of the metropolitan region (hereafter the ‘ring’ district). By integrating Multi-way Factor Analysis with Continuous Wavelength Transform and rapidity-of-change metrics grounded on complex thinking, the exploratory approach proposed here has delineated latent mechanisms of urban expansion, indicating substantial divergences in the development path of the two districts. While the ‘core’ district experienced population increase and settlement densification, the ‘ring’ district underwent a suburbanization process resulting in a moderate—and relatively slow—concentration of economic activities and social functions. Reflecting a non-linear propagation of growth impulses from urban to rural areas, the economic interplay between ‘core’ and ‘ring’ areas delineates a complex development path accelerating spatial polarization in central and peripheral locations. Our results definitely highlight the importance of ‘system thinking’ in regional studies, applied economics, and social research.

Influence of the Crack Angle on the Deformation and Failure Characteristics of Sandstone under Stepped Cyclic Uniaxial Compression with a Constant Lower Limit

Engineering rock structures containing joints and fissures are frequently subjected to discontinuous periodic disturbances of varying amplitudes. To attain the quantitative relationship between the crack angle and the mechanical and deformation properties of rock under complex stress paths, uniaxial cyclic loading and unloading tests with increasing stress gradients were conducted on sandstone specimens containing a single crack of different angles. Our results showed that the bearing capacity of the sandstone increased as the crack angle increased. The irreversible strain and elastic moduli of the rock presented a sudden increase when entering the next cycle of the stepped loading. However, the entire loading process can be divided into three stages according to their respective trends. These three stages correspond to the three stages of rock deformation, i.e., the pore crack compaction stage, the elastic deformation to the stable micro-elastic crack development stage, and the unstable crack development stage. In addition, the crack angle of sandstone showed a negative correlation with the irreversible strain, but a positive correlation with the elastic modulus. With the increasing crack angle, the failure mode of the rock changed from the tensile-shear failure to the shear failure, and then to the interlayer dislocation failure.

Analysing Multiple Paths of Urban Low-Carbon Governance: A Fuzzy-Set Qualitative Comparative Analysis Method Based on 35 Key Cities in China

The city is a crucial space carrier for the country to carry out low-carbon construction and solve sustainable–development problems. However, existing research lacks an in-depth discussion of the complex mechanisms and governance paths of urban low-carbon transformation. Therefore, this study explores multiple paths of urban low-carbon governance (ULCG). This study constructs a theoretical model of ULCG based on the technology–organisation–environment (TOE) framework. It uses fuzzy-set qualitative comparative analysis (fsQCA) to analyse the overall and sub-regional paths of 35 key cities in China to explore various ULCG approaches. The following three conclusions are drawn. First, a single antecedent condition is not a necessary condition for ULCG. Second, five differentiated paths have been formed under the joint action of the TOE conditions to improve ULCG. It can be divided into three types: the ULCG model dominated by ‘big data + market’, ‘big data’, and ‘market’. Third, apparent differences exist in the ULCG paths in China’s eastern, central and western regions. The study deepens the rational understanding of multiple factors interacting in the complex mechanism behind urban low-carbon transformation and provides differentiated ULCG paths, enabling cities in eastern, central, and western China to choose low-carbon governance paths tailored to their local conditions based on both a comprehensive perspective and a regional perspective.

One size does not fit all: an exploratory interview study on how translational researchers navigate the current academic reward system.

Translational research is a subfield of the biomedical life sciences that focuses on clinically driven healthcare innovations. The workforce of this subfield, i.e., translational researchers, are diversely specialized and collaborate with a multitude of stakeholders from diverse disciplines in and outside academia in order to navigate the complex path of translating unmet clinical needs into research questions and ultimately into advancements for patient care. Translational researchers have varying responsibilities in the clinical, educational, and research domains requiring them to split their time two- or three-ways. Working between these domains and alongside peers who do not split their time as such, raises questions about the academic reward system used to recognize their performance, which mainly focuses on publication metrics within the research domain. What is unclear is how combining research tasks with tasks in the clinical and/or educational domains effects translational researchers and how they navigate the academic reward system. In this exploratory interview study, semi-structured interviews were conducted to gain a deeper understanding of the current academic reward system for translational researchers. Stratified purposeful sampling was used to recruit 14 translational researchers from varying countries, subspecialties, and career stages. The interviews were coded after data collection was complete and arranged into three overarching result categories: intrinsic motivation, extrinsic factors, and ideal academic reward system and advice. We found that these 14 translational researchers were intrinsically motivated to achieve their translational goals while working in settings where clinical work was reported to take priority over teaching which in turn took priority over time for research. However, it is the latter that was explained to be essential in the academic reward system which currently measures scientific impact largely based on publications metrics. In this study, translational researchers were asked about their thoughts regarding the current academic reward system. Participants shared possible structural improvements and ideas for specialized support on an individual, institutional, and also international level. Their recommendations focused on acknowledging all aspects of their work and led to the conclusion that traditional quantitative academic reward metrics do not fully align with their translational goals.

Phase change heat transfer analysis of anisotropic structures with moving heat source using the element-free Galerkin method

The computational model of phase change heat transfer analysis for anisotropic structures with moving heat sources is established using the element-free Galerkin method (EFGM), and the accuracy and superiority of the proposed model are verified by experimental results and two butt welding examples of anisotropic plates. The influence of off-angle and thermal conductivity factors on the temperature field, welding pool, and weld seam is investigated. The results show that EFGM temperature and welding pool have higher accuracy compared with the finite element method solutions. It is demonstrated that EFGM has a distinct advantage in the tracing of moving heat sources and dynamic phase interfaces during the butt welding process, whether along straight or complex paths. There is a high-quality welding pool and a uniform temperature in butt welding of anisotropic structures compared with isotropic structures. The increase of thermal conductivity factor can accelerate the phase change process and its reasonable range is suggested to be 2–4. It can reduce the temperature concentration and accelerate the solidification speed of weld seam when the off-angle is enlarged, and its recommended range is 30°–45°.

Design and Simulation of a Neuroevolutionary Controller for a Quadcopter Drone

The problem addressed in the present paper is the design of a controller based on an evolutionary neural network for autonomous flight in quadrotor systems. The controller’s objective is to govern the quadcopter in such a way that it reaches a specific position, bearing on attitude limitations during flight and upon reaching a target. Given the complex nature of quadcopters, an appropriate neural network architecture and a training algorithm were designed to guide a quadcopter toward a target. The designed controller was implemented as a single multi-layer perceptron. On the basis of the quadcopter’s current state, the developed neurocontroller produces the correct rotor speed values, optimized in terms of both attitude-limitation compliance and speed. The neural network training was completed using a custom evolutionary algorithm whose design put particular emphasis on the cost function’s definition. The developed neurocontroller was tested in simulation to drive a quadcopter to autonomously follow a complex path. The obtained simulated results show that the neurocontroller manages to effortlessly follow several types of paths with adequate precision while maintaining low travel times.

Structure and Migration Mechanisms of Small Vacancy Clusters in Cu: A Combined EAM and DFT Study.

Voids in face-centered cubic (fcc) metals are commonly assumed to form via the aggregation of vacancies; however, the mechanisms of vacancy clustering and diffusion are not fully understood. In this study, we use computational modeling to provide a detailed insight into the structures and formation energies of primary vacancy clusters, mechanisms and barriers for their migration in bulk copper, and how these properties are affected at simple grain boundaries. The calculations were carried out using embedded atom method (EAM) potentials and density functional theory (DFT) and employed the site-occupation disorder code (SOD), the activation relaxation technique nouveau (ARTn) and the knowledge led master code (KLMC). We investigate stable structures and migration paths and barriers for clusters of up to six vacancies. The migration of vacancy clusters occurs via hops of individual constituent vacancies with di-vacancies having a significantly smaller migration barrier than mono-vacancies and other clusters. This barrier is further reduced when di-vacancies interact with grain boundaries. This interaction leads to the formation of self-interstitial atoms and introduces significant changes into the boundary structure. Tetra-, penta-, and hexa-vacancy clusters exhibit increasingly complex migration paths and higher barriers than smaller clusters. Finally, a direct comparison with the DFT results shows that EAM can accurately describe the vacancy-induced relaxation effects in the Cu bulk and in grain boundaries. Significant discrepancies between the two methods were found in structures with a higher number of low-coordinated atoms, such as penta-vacancies and di-vacancy absortion by grain boundary. These results will be useful for modeling the mechanisms of diffusion of complex defect structures and provide further insights into the structural evolution of metal films under thermal and mechanical stress.

Strain-Induced Phase Transformation Modeling of QP980 Steel and Its Application to Complex Loading Paths

Quenching and partitioning (QP) steel has attracted much focus due to the effect of phase transformation induced plasticity (TRIP). However, the TRIP behavior makes it difficult to accurately predict the strain and stress distribution as well as the phase transformation behavior of QP steel. Scanning electron microscope (SEM) images of the QP980 microstructure were produced in this study, characterized by a combination of lath martensite, polygonal ferrite and retained austenite. The volume fraction evolution of retained austenite with equivalent plastic strain (EPS) of uniaxial tension was obtained by electron-backscatter diffraction. The phase transformation kinetics equations of QP980 were deduced based on the phase transformation model proposed by Olson and Cohen (simplified as O-C theory), considering the effects of strain rate, deformation temperature and stress state. A constitutive model on the dependence of the phase transformation was proposed to reveal the relation between metallographic characteristics and mechanical performance of QP980 steel during deformation. The User subroutine VUMAT in ABAQUS/Explicit was implemented to describe the volume fraction of retained austenite (VFRA) under different stress states. The established phase transformation and constitutive model were applied to three kinds of complex path loading tests. The variation in the retained austenite under complex strain paths was obtained and compared with the experimental results.

Digital Tools in Contemporary Theatre Practice

The relevance of this article is substantiated by the fact that contemporary theatrical art is on a complex and active path of experimentation, competing with the basic principles of classical theatrical staging. It is therefore necessary to consider in detail the technologies that are involved and rapidly being introduced in the practice of modern theatre. The purpose of this article is to analyse the use of digital tools in the practice of modern theatre art, which makes theatre in today's realities more demanding. The theoretical analysis of scientific literature, the historical method, the comparative method, the typological and systemic method, and the generalisation of theoretical and practical experience of the modern theatre were chosen as the main methods of cognition in this study. It was concluded that the modern theatre, through the use of digital technology, has been enriched with current technical concepts and formats. The practical value of the research consists in the fact that the materials analysed in the article can serve as an informative basis for training and retraining of specialists in the field of theatre education.

Strain induced crystallization of PET under biaxial conditions. From laboratory tests to injection stretch-blow molding

Conventional biaxial testing and free stretch blow molding (ISBM) of preforms were conducted in parallel to analyze the biaxial behavior of PET and the resulting strain-induced crystallization (SIC) under bi-axial conditions. Stretch blowing has promoted complex loading paths combining most of the simple paths used at the laboratory scale, which are analyzed locally using marked preforms. The time-temperature superposition principle is shown to apply under biaxial conditions up to high strain, which has facilitated the definition of experimental sets and mechanical comparisons. X-ray diffraction was used to analyze the crystal microstructure and texture. In ISBM, the texture is not a simple image of the final deformation state in terms of orientation. The organized phase that is induced is probably an imperfect crystal capable of evolving in time and the strain hardening under biaxial conditions could be a gradual phenomenon as in uniaxial stress. A scenario is proposed.

AlphaFold predicts novel human proteins with knots.

The fact that proteins can have their chain formed in a knot is known for almost 30 years. However, as they are not common, only a fraction of such proteins is available in the Protein Data Bank. It was not possible to assess their importance and versatility up until now because we did not have access to the whole proteome of an organism, let alone a human one. The arrival of efficient machine learning methods for protein structure prediction, such as AlphaFold and RoseTTaFold, changed that. We analyzed all proteins from the human proteome (over 20,000) determined with AlphaFold in search for knots and found them in less than 2% of the structures. Using a variety of methods, including homolog search, clustering, quality assessment and visual inspection, we determined the nature of each of the knotted structures and classified it as either knotted, potentially knotted, or an artifact, and deposited all of them in a database available at: https://knotprot.cent.uw.edu.pl/alphafold. Overall, we found 51 credible knotted proteins (0.2% of human proteome). The set of potentially knotted structures includes a new complex type of a knot not reported in proteins yet. That knot type, denoted 63 in mathematical notation, would necessitate a more complex folding path than any knotted protein characterized to date. This article is protected by copyright. All rights reserved.

Path planning for graded concrete element fabrication

AbstractThe technology of functionally graded concrete (FGC) is a new methodology in the field of concrete construction, striving for mass savings by adjusting the elements interior design. A promising approach herein is meso-gradation, where concrete hollow spheres are placed inside the formwork before casting the element; this allows up to 50% mass savings without a loss in load-bearing capacity, whilst also ensuring recyclability compared to e.g. bubble decks. In order to prevent damage/displacement of the spheres during automated fabrication, the extruded concrete flow must avoid the spheres, whilst neatly covering the elements area in order to prevent cavities. Both requirements formulate a complex path planning problem that must be solved in order to achieve automated fabrication. In this paper, we propose a method for solving this problem, which is based on theoretical findings on Hamiltonian triangulations. Our approach is based on the idea that the elements area is triangulated, such that all sphere centers are corners of triangles. For each triangle, a smooth path can be planned straightforwardly on a consideration of the geometry, such that the global path is made of a sequence of local ones. This necessitates finding a triangulation that is hamiltonian, i.e. a sequence where all triangles are visited exactly once. To this end, we first present a new class of triangulations and proof their hamiltonicity, followed by an algorithm that generates such triangulations on certain FGC element geometries. This is followed by the local path planning problem, whose special structure with start/end tangential and curvature constraints facilitates the use of a polar coordinate approach.

Study on wetting deformation model of coarse-grained materials based on P-Z model and BP neural network

The wetting deformation of coarse-grained materials can seriously affect the safety of earth and rock dams during initial water storage. The wetting model formulas are expressed in various forms and have complex parameters. Only a small amount of test data is fitted by mathematical statistics, and the universality of the obtained wetting model is unknown. Duncan-Chang E-B constitutive model cannot accurately reflect the wetting deformation characteristics of coarse-grained materials. Through the double-line wetting test of coarse-grained materials, the wetting model proposed by predecessors was verified and analyzed. Based on the indoor wetting test data, the parameters of each wetting model were fitted to analyze the accuracy of each wetting model in describing the wetting deformation characteristics. According to the P-Z model in the elastic-plastic theory and the wetting model formula, the P-Z wetting model is established, and the BP artificial neural network is introduced to establish the artificial neural network wetting deformation prediction model based on the P-Z model. The results show that the relationship between wetting axial strain and wetting stress level is best expressed by the exponential function. The relationship between wetting volumetric strain and wetting stress level is best described by Cheng’s linear function. The relative errors between the predicted and experimental values of the proposed neural network prediction model are all within 6%. The relationship between wetting axial strain and wetting stress level is exponential function, and the relationship between wetting volumetric strain and wetting stress level is linear function. The P-Z wetting model proposed in this research can better reflect the wetting deformation characteristics of coarse-grained materials under complex stress paths. The artificial neural network prediction model based on P-Z wetting model is more reliable and accurate, which can meet the prediction requirements of actual engineering for wetting deformation of coarse-grained materials.

Three-dimensional mesoscopic simulation of radiative transfer in graded index media

Light propagation in three-dimensional (3D) graded index (GRIN) media has a complex spatial path, making it difficult to solve thermal radiative transfer problems. In this paper, a mesoscopic lattice Boltzmann method (LBM) that implements simple steady-state and transient radiative transfer solutions in 3D GRIN media is proposed. During the construction of the lattice Boltzmann (LB) model, the concept of the “local radiative transfer direction”, which addresses complex curved trajectories in 3D GRIN media simply, is introduced. The radiative transfer equation of 3D GRIN media can be strictly recovered from the LB model by adopting the Chapman-Enskog analysis. Numerical results indicate that radiative transfer problems in 3D GRIN media can be solved effectively by the LBM. Additionally, the influences of different optical parameters on steady-state and transient radiative transfer in 3D GRIN media are discussed. The LBM is a promising mathematical tool for radiative transfer in 3D GRIN media.

Transforming Industrial Manipulators via Kinesthetic Guidance for Automated Inspection of Complex Geometries.

The increased demand for cost-efficient manufacturing and metrology inspection solutions for complex-shaped components in High-Value Manufacturing (HVM) sectors requires increased production throughput and precision. This drives the integration of automated robotic solutions. However, the current manipulators utilizing traditional programming approaches demand specialized robotic programming knowledge and make it challenging to generate complex paths and adapt easily to unique specifications per component, resulting in an inflexible and cumbersome teaching process. Therefore, this body of work proposes a novel software system to realize kinesthetic guidance for path planning in real-time intervals at 250 Hz, utilizing an external off-the-shelf force-torque (FT) sensor. The proposed work is demonstrated on a 500 mm2 near-net-shaped Wire-Arc Additive Manufacturing (WAAM) complex component with embedded defects by teaching the inspection path for defect detection with a standard industrial robotic manipulator in a collaborative fashion and adaptively generating the kinematics resulting in the uniform coupling of ultrasound inspection. The utilized method proves superior in performance and speed, accelerating the programming time using online and offline approaches by an estimate of 88% to 98%. The proposed work is a unique development, retrofitting current industrial manipulators into collaborative entities, securing human job resources, and achieving flexible production.

Recognition of pick wear condition based on Grey-Markov chain model

1. Bagri S., Manwar A, Varghese A., Mujumdar S., Joshi S.S., 2021, Tool wear and remaining useful life prediction in micro-milling along complex tool paths using neural networks, Journal of Manufacturing Processes, 71, 679-698. CrossRef Google Scholar

A Large-Scale Characterization of How Readers Browse Wikipedia

Despite the importance and pervasiveness of Wikipedia as one of the largest platforms for open knowledge, surprisingly little is known about how people navigate its content when seeking information. To bridge this gap, we present the first systematic large-scale analysis of how readers browse Wikipedia. Using billions of page requests from Wikipedia’s server logs, we measure how readers reach articles, how they transition between articles, and how these patterns combine into more complex navigation paths. We find that navigation behavior is characterized by highly diverse structures. Although most navigation paths are shallow, comprising a single pageload, there is much variety, and the depth and shape of paths vary systematically with topic, device type, and time of day. We show that Wikipedia navigation paths commonly mesh with external pages as part of a larger online ecosystem, and we describe how naturally occurring navigation paths are distinct from targeted navigation in lab-based settings. Our results further suggest that navigation is abandoned when readers reach low-quality pages. Taken together, these insights contribute to a more systematic understanding of readers’ information needs and allow for improving their experience on Wikipedia and the Web in general.

A critical-place ethnography of transfronterizo teachers at the intersections of self-defense, self-creation, and borderlands identity formation

ABSTRACT Teacher identity work throughout one’s academic studies and career has been shown to have a positive impact on teachers’ resilience and longevity in the field, in contrast to those who do not engage in these kinds of reflexive practices. This research expands our understanding of teacher identities and how they develop within and outside school settings, acknowledging the complex paths teachers navigate to enter the classroom. To promote reflexive thinking among pre-service and in-service teachers about their identities, how they inform their desire to teach and their instructional practices, this inquiry presents an account of teachers who were at one time transfrontertizos – when they were students, they crossed the border from Mexico to attend U.S. schools. Drawing from ethnographic research conducted in Calexico and its neighbouring city of Mexicali, it explores how their experiences of crossing back and forth between two countries for education shaped their identities in distinct ways.