bluuebunny/crossref_metadata_2025 huggingface dataset:
E-learning for smart-universities: pandemic challenges and opportunities in Morocco
Authors: Anigri Mohamed
Published: September 2021

Both ICT and internet have become a vital part of citizens’ daily lives. In fact, many aspects of cities, including culture, economy, education have become closely linked to ICT. Accordingly, the concept of the smart city has emerged to attract the interest of governments, companies, educational institutions and Universities [1]. In Morocco, most universities or higher education institutions have always been interested in keeping up with the fast-paced world of technology and integrate ICT in mainstream education. However, most attempts to initiate smart universities is always faced with a series of challenges and constraints. Most of which are related to lack of infrastructure, students’ and professors’ lack of technological readiness, and socio-economic inequality among students. Most recently, due to COVID-19, universities are forced to resort to emergency remote learning and scramble different options of e-learning as a dire need to tackle the current educational crisis which creates a certain chaos due to lack of readiness to an advanced technological application. This paper is an attempt to discuss the challenges posed and opportunities offered using e-learning to deal with the new normal (Covid-19) in different educational levels in general and higher education in particular. Significantly, this paper reviews most of that has been said about online learning, describes some of the conducted empirical studies, and calls for implementing e-learning as an innovative teaching strategy for smart universities.
Modeling techniques for decentralized energy systems applied in smart grids
Authors: El Assri Nasima , Chabaa Samira , Lmesri Khadija , Jallal Mohammed Ali , Zeroual Abdelouhab
Published: September 2021

Historically, power grids have emerged as the most economical way to match diversified generation resources. After the Second World War, all advanced countries chose to develop a centralized electrical system to transport energy throughout the national territory and then distribute it to the various points of consumption. In this centralized management, production is adapted to an ever-increasing demand, driven by economic and demographic developments. Gradually, the consumption profile has changed: the development of electrical uses (particularly heating and air conditioning), leading to consumption peaks that are increasingly difficult to satisfy. The appearance of the electric vehicle reinforces these growing imbalances between supply and demand. Thus, the production profile has gradually changed: production has moved closer to the places of consumption but has become more variable, such as wind and solar energy (known as intermittent sources of energy production). In this transforming energy view, these historical centralized and unidirectional networks reach saturation and need to be modernized by turning to a decentralized model. In this perspective, the development of smart grids (SG) is taking place. This paper aims to define decentralized energy systems that provide various benefits and cause significant challenges. Finally, we propose several techniques that are highly efficient in modeling and controlling smart grid systems in order to help decision-makers to address complex problems.
Three Level Heterogeneous Zonal Stable Election Protocol for Energy Efficiency in Wireless Sensor Networks
Authors: Benelhouri Abdelkader , Idrissi-Saba Hafida , Antarir Jilali
Published: September 2021

Sensor battery limitation has always been the most challenging hurdle for wireless sensor networks. Many energy effcient routing protocols have been proposed to overcome this issue in homogeneous networks where sensor nodes start with the same initial energy. When sensor nodes have different amount of initial energy, the network is heterogeneous and it becomes complicated to design an energy effcient routing protocol to save nodes energy and prolong network lifetime. Herein, we propose a three level heterogeneous routing protocol to boost network stability period of wireless sensor networks. The network model splits up into five zones according to nodes initial energies and distance to base station. For data communication, the proposed model relies on two types of communications: Direct and Multi-Hop. The choice of the type of communication is made according to nodes initial energy and their distance to the base station. The clustering scheme is used just in the zones that contains nodes with higher energies. The simulation of our proposed scheme is done using Matlab simulator and the results are compared to the conventional heterogeneous routing protocols 3-level heterogeneous Stable Election Protocol and 3-level Modified Low Energy Adaptive Clustering Hierarchy.
The political economy of sharing
Authors: Bogomolov Evgenii , Orusova Olga , Ekaterinovskaya Maria
Published: September 2021

The widespread adoption of a new model of economy – the economy of shared consumption (public services for short-term rental of bicycles, cars, apartments, houses, other goods and services) – has raised many questions for the economic theory. What is a shared economy? What are the reasons for its appearance in different countries? How does it change property relations? What is its future? The answers to these questions are considered using the publications of Russian and foreign scientists. The authors conclude that sharing economy is just a new variant of capital system adaptation.
Energy investments in renewable energy sources as a way towards enterprises’ sustainable development
Authors: Poszwa Greta
Published: September 2021

Sustainable development is a pervasive philosophy that every participant in the global economy (including consumers and government) must agree with if today’s needs are to be met without risking the ability of future generations to meet their own. According to this premise, the idea of sustainable development cannot be implemented by a single enterprise (or even the entire business community) in isolation. In their activities, business entities wanting to apply the philosophy of the balanced use of all resources necessary in the production process should take into account the assumptions included in the seventeen priority goals of sustainable development in the decision-making process. This article shows how enterprises can both achieve business goals and focus on environmental protection through the implementation of energy investments. However, it also shows that the mere awareness of the need to implement energy investments in their organizations is not sufficient to achieve these goals, and the level of investments in this respect among small and medium-sized enterprises is moderate.
Managing sustainability of national security: Implications for Ukraine
Authors: Todorov Ihor , Todorova Nataliia
Published: September 2021

The article studies the interrelated categories of national security and sustainable development, which are currently the object of special attention of government institutions, civil society, political parties, territorial communities, etc. The purpose of the study is to specify the topical issues associated with sustainable development of the national security, building on the international experience in this area, and to determine the locally adaptable ways of ensuring sustainability of the national security of Ukraine. The process of sustainable development of national security is to be more effective when there is a clear idea of its structural and functional elements, direct and indirect ties among them. The synergy of national security with the implementation of the 2030 Sustainable Development Goals is able to ensure comprehensive modernization in accordance with today’s requirements and strengthen the level of welfare and security of citizens. The integrated level of national security of Ukraine correlates with the goals of sustainable development. The country’s stability and its resistance to national security threats is a necessary condition for implementing a purposeful sustainable development strategy for 2030. Successful implementation of sustainability tasks for Ukraine is possible provided there exist unity and capacity of state power and society.
Evolutionary development of energy efficiency in the context of the national carbon-free economic development
Authors: Ziabina Yevheniia , Pimonenko Tetyana , Lyulyov Oleksii , Us Yana , Proshkin Dmytro
Published: September 2021

This research aims to analyse the evolutionary development of the scientific treatises devoted to the national economic energy efficiency. To attain the paper’s goal, this study is carried out in the following logical sequence: 1) identification and generation of the necessary relevant data: 2) analysis of keywords co-occurrence to determine the promising research areas on energy efficiency. The authors used keywords “energy policy”, “energy efficiency”, “sustainable development” to generate the relevant study sample. Thus, the study sample consists of 48,888 publications indexed by the scientometric databases Scopus and Web of Science. The study period is 2000-2020. Visualization of the bibliometric analysis results concerning the national economic energy efficiency management was conducted using the VOSviewer software v.1.6.10. The co-occurrence network map identified the six stages of evolutionary development of scientific treatises on the national economic energy efficiency. Besides, the authors applied Google Trends tools to analyse 2,172 internet search queries regarding the social concern in energy efficiency. In the study, the authors conclude that the scientific society has not yet reached a consensus in identifying key determinants of energy efficiency under the national economy transition to a carbon-free development model. The research results can be helpful for scholars investigating the determinants of developing the national economic energy efficiency.
To wish you well: the biopolitical subjectivities of medical crowdfunders during and after Aotearoa New Zealand’s COVID-19 lockdown
Authors: Wardell Susan
Published: September 2021

Crowdfunding platforms apply a marketized, competitive logic to healthcare, increasingly functioning as generative spaces in which worthy citizens and biopolitical subjects are produced. Using a lens of biopower, this article considers what sort of biopolitical subjectivities were produced in and through New Zealand crowdfunding campaigns during the 2020 COVID-19 lockdown. It focuses on a discursive and dialogical analysis of 59 online medical crowdfunding campaigns that were active during lockdown and chose to mention the pandemic. These pages pointed to interrelated biological, social and economic precarities, speaking to questions about how citizens navigate uneven needs during uncertain times. Findings showed that crowdfunders referred to the pandemic in order to narrate their own situation in culturally coherent ways and to establish context-specific relations of care. This included contextualising their needs through establishing shared crisis narratives that also made the infrastructural contexts of healthcare visible and performing relational labour in ways that aligned with nationally specific affective regimes. By highlighting their own vulnerability, crowdfunders strategically mobilised broader lockdown discourses of self-sacrifice on behalf of vulnerable people. In this way, New Zealand’s lockdown produced subjectivities both drawing on wider neoliberal moral regimes and specific to the nuanced and emergent moral systems of pandemic citizenship.
Phase lag index-based graph attention networks for detecting driving fatigue
Authors: Wang Zhongmin , Zhao Yupeng , He Yan , Zhang Jie
Published: September 2021

It is important to understand the changes in the characteristics of the brain network in the state of driving fatigue and to reveal the pattern of functional connectivity between brain regions when fatigue occurs. This paper proposes a method for the detection of driving fatigue based on electroencephalogram (EEG) signals using a phase lag index graph attention network (PLI-GAT). Phase synchronization between EEG signals is a key attribute for establishing communication links among different regions of the brain, and so, the PLI is used to construct a functional brain network reflecting the relationship between EEG signals from different channels. Multi-channel EEG time–frequency features are then modeled as graph data, and the driving fatigue monitoring model is trained using a GAT. Compared with traditional graph neural networks, the GAT applies an aggregation operation to adjacent EEG channel features through the attention mechanism. This enables the adaptive assignment of different neighbor weights, which greatly improves the expressiveness of the graph neural network model. The proposed method is validated on the publicly available SEED-VIG dataset, and the accuracy of fatigue state recognition is found to reach 85.53%. The results show that the functional connectivity among different channels is significantly enhanced in the fatigue state.
Plasma transport simulations of Rayleigh–Taylor instability in near-ICF deceleration regimes
Authors: Vold E. , Yin L. , Albright B. J.
Published: September 2021

Rayleigh–Taylor (R–T) instability between plasma species is examined in a kinetic test and near-inertial confinement fusion (ICF) regimes. A transport approximation to the plasma species kinetics is used to represent viscosity and species mass transport within a hydrodynamic fluid code (xRage). R–T simulation results are compared in a kinetic test regime with a fully kinetic particle-in-cell approach [vectorized particle-in-cell (VPIC)] and with an analytic model for the growth rate of R–T instability. Single-mode growth rates from both codes and the analytic model are in reasonable agreement over a range of initial wavelengths including the wavenumber of maximum growth rate. Both codes exhibit similar diffusive mixing fronts. Small code-to-code differences arise from the kinetics, while simulation-analytic model differences arise from several sources dominated by the choice of gradients establishing the hydrostatic equilibrium initial conditions. After demonstrating code agreement in the kinetic test regime, which is practically accessible to the VPIC code, then the xRage code, with the fluid plasma transport approximation, is applied to single mode R–T instability under deceleration conditions closer to an ICF implosion, approximated with a carbon (C) shell imploding on a deuterium (D) fuel. The analytic wavelength of maximum instability is limited by the kinetics, primarily in the viscosity, and is found to be ≈10 μm for an ion temperature near 1 keV at this C–D interface, with the most unstable wavelength increasing as temperature increases. The analytic viscous model agrees with simulation results over a range of initial perturbation wavelengths, provided the simulation results are analyzed over a sufficiently short duration (⪅0.2 ns in this case). Details of the fluid structure evolution during this R–T deceleration are compared between the inviscid Euler equations and cases, which include plasma transport over a range in initial wavelengths and initial perturbation amplitudes. The inviscid Euler solutions show a grid-dependent cascade to smaller scale structures often seen in the R–T instability, while simulations with plasma transport in this deceleration regime develop a single vortex roll-up, as the plasma transport smoothes all hydrodynamic fluid structures smaller than several micrometers. This leads to a grid-converged transient solution for the R–T instability when kinetic effects are included in the simulations, and thus represents a direct numerical simulation of the thermal ions during R–T unstable mixing in ICF relevant conditions.
Mechanisms of long-range edge retraction of metal bilayer films
Authors: Jamadagni Bhagyashree , van Benthem Klaus
Published: September 2021

The agglomeration of thin films on substrates is driven by minimization of the free surface and film/substrate interface energies and has been studied extensively for single component metal films. Only a few studies have investigated the agglomeration of kinetically constrained metal bilayer films, for which unusual long-range edge retraction was recently reported. This study has explored the agglomeration of kinetically constrained thin films of Au and Ni that were subsequently deposited on SiO2/Si substrates and annealed under high vacuum conditions at 545, 675, and 730 °C. Long-range edge retraction of the metal bilayer films revealed seven regions across the receding edge that are microstructurally distinct. The absolute and relative widths of the regions depend on the deposition sequence of the two metal films and annealing temperature. Arrhenius analysis of growth rates for different regions was used to identify energy barriers for mass transport mechanisms. The presence of native nickel oxide was found to have a significant effect on the kinetics of long-range edge retraction. The experimental results suggest that the formation of multiple regions across the receding edge is part of the kinetic evolution of long-range edge retraction of metal bilayer films.
Electron and hole mobilities of GaN with bulk, quantum well, and HEMT structures
Authors: Hamaguchi Chihiro
Published: September 2021

Electron and hole mobilities of GaN are calculated for three-dimensional (3D, bulk) and two-dimensional [2D, quantum well (QW), and HEMT] structures, including scattering processes of acoustic deformation potential, polar optical phonon, piezoelectric, ionized impurity, and so on. The calculated mobilities for 2D structures are strongly dependent on quantum well structures and impurity densities, although the temperature dependence of the mobilities behaves in a similar way to bulk values. In the present analysis, energy band structures of GaN are calculated by the empirical pseudopotential method including spin–orbit interaction, and then the electron effective mass of the conduction band and the hole effective masses of the valence bands are evaluated, which are used for the calculations of electron and hole mobilities. The calculated valence band structure of the heavy, light, and crystal field splitted valence bands reveal complicated dispersion due to the spin–orbit interaction. The obtained electron effective mass mc=0.145m is isotropic, and the heavy hole effective mass in the c∥ plane is mhh∥=1.20m, while in the c⊥ plane, the band edge effective mass is mhh0⊥=0.55m and the over all fitted heavy hole effective mass is mhh⊥=1.20m. The light hole effective masses are mlh∥=1.35m and mlh⊥=0.165m. Both of the electron and hole mobilities are limited by ionized impurity scattering at low temperatures and by polar optical phonon scattering at high temperatures. Calculated electron mobilities are 7100 cm2/Vs for bulk, 4600 cm2/Vs for high electron mobility transistor (HEMT), and 3600 cm2/Vs for QW at room temperature and calculated hole mobilities are 450 cm2/Vs for bulk, 450 cm2/Vs for HEMT, and 500 cm2/Vs for QW at room temperature. All the expressions for scattering rates and respective mobilities are derived for 3D and 2D (QW and HEMT) structures and enable readers to calculate electron and hole mobilities in different structures with parameters given in the table or modified ones.
Effects of chain length on Rouse modes and non-Gaussianity in linear and ring polymer melts
Authors: Goto Shota , Kim Kang , Matubayasi Nobuyuki
Published: September 2021

The dynamics of ring polymer melts are studied via molecular dynamics simulations of the Kremer–Grest bead-spring model. Rouse mode analysis is performed in comparison with linear polymers by changing the chain length. Rouse-like behavior is observed in ring polymers by quantifying the chain length dependence of the Rouse relaxation time, whereas a crossover from Rouse to reptation behavior is observed in linear polymers. Furthermore, the non-Gaussian parameters of the monomer bead displacement and chain center-of-mass displacement are analyzed. It is found that the non-Gaussianity of ring polymers is remarkably suppressed with slight growth for the center-of-mass dynamics at long chain length, which is in contrast to the growth in linear polymers for both the monomer bead and center-of-mass dynamics.
Mechanical behavior of single layer MoS2 sheets with aligned defects under uniaxial tension
Authors: Han Yekun , Chen Peijian , Zhu Jiaming , Liu Hao , Zhang Yingying
Published: September 2021

Compared with a single defect or randomly distributed defects, aligned defects are widely found or artificially designed in structures to realize various functions. However, the mechanical behavior of transition metal dichalcogenides with aligned defects is still unclear, which restricts the blooming application in novel flexible nanodevices. Herein, we report the strength and fracture properties of single layer MoS2 (SLMoS2) sheets with aligned defects under uniaxial tension by numerical calculation and theoretical modeling. It is found that the increase of the number of defects and adjacent spacing leads to the decrease of critical strain as well as tensile strength of both pristine and kirigami MoS2 sheets. Three types of crack propagation phenomena are discovered, and an effective theoretical model is employed to uncover the underlying mechanism of crack deflection phenomenon in SLMoS2 sheets with aligned defects. These results provide important insights into mechanical behavior of SLMoS2 sheets and should be helpful for potential applications of the new two-dimensional material.
High-speed 2D and 3D mid-IR imaging with an InGaAs camera
Authors: Potma Eric O. , Knez David , Ettenberg Martin , Wizeman Matthew , Nguyen Hai , Sudol Tom , Fishman Dmitry A.
Published: September 2021

Recent work on mid-infrared (MIR) detection through the process of non-degenerate two-photon absorption (NTA) in semiconducting materials has shown that wide-field MIR imaging can be achieved with standard Si cameras. While this approach enables MIR imaging at high pixel densities, the low nonlinear absorption coefficient of Si prevents fast NTA-based imaging at lower illumination doses. Here, we overcome this limitation by using InGaAs as the photosensor. Taking advantage of the much higher nonlinear absorption coefficient of this direct bandgap semiconductor, we demonstrate high-speed MIR imaging up to 500 fps with under 1 ms exposure per frame, enabling 2D or 3D mapping without pre- or post-processing of the image.
Effects of localization length and spatial disorder on a charge carrier mobility in organic disordered semiconductors
Authors: Shukri Seyfan , Deja Lemi
Published: September 2021

We investigate the transport properties of charge carrier disordered organic semiconductors with a focus on the determination and analysis of charge carrier mobility. By understanding that charge transport is due to incoherent hopping of charge carriers across localized states, we use a model that relates mobility to charge carrier (not small polarons) hopping by thermal activation. We consider the Miller–Abrahams expression to describe the hopping rate of charge carriers and employ kinetic Monte Carlo simulation methods to generate data from which we can analyze charge carrier mobility as a function of applied electric field, temperature, localization length, and spatial and energetic disorder parameters. Based on our results, we discuss the effects of these parameters on charge carrier mobility. Our results show the importance of the spatial disorder parameter and localization length in the effects of electric field dependence on charge carrier mobility, and we also evaluate the value of localization length that has been mostly considered as 0.1b, where b is the lattice parameter.
Investigation on flow around and through a hygroscopic porous cylinder with consideration of compressibility of moist air
Authors: Sun Junjun , Zhu Qingyong
Published: September 2021

In order to better understand the influence of the physical conditions, such as high temperature, high humidity, and high speed, on porous media in coastal engineering, a compressible, viscous, unsteady flow around and through a hygroscopic porous circular cylinder was discussed in this paper. The effects of the hygroscopicity, the Mach number, and the Darcy number on the flow structure, temperature field, and water content of the porous cylinder are evaluated in detail. The results of numerical simulations show significant effects of compressibility of moist air on the lift and drag of the cylinder. With an increase in the Mach number, the frequency of vortex shedding argument and dimensionless lift and drag of the porous cylindrical surface decrease. Nevertheless, the effect of the Mach number on the magnitude of the vorticity and distribution of temperature is negligible. In our simulation, we also found that an increase in the Darcy number significantly weakens the magnitude of the vorticity and the amplitude of lift and drag of the cylinder. Moreover, the absorption of the porous cylinder may also have a weak effect on accelerating vortex shedding. Considering the high temperature, high humidity, and high speed of the coastal environment, this paper has some significance for the study of wind erosion.
TCRβ rearrangements without a D segment are common, abundant, and public
Authors: de Greef Peter C. , de Boer Rob J.
Published: September 2021

Significance

The human body detects foreign pathogens by T cells with specific receptors. These are not directly encoded in the genome but generated in a random process that combines small gene segments into functional subunits of the receptor. The

β

-chain of the T cell receptor is normally composed of three such gene segments. Here we identify a group of T cells that lack the middle segment in their receptor sequence. We find that such sequences are mostly generated before birth, persist over a human lifetime, and, as a result, are excessively shared between individuals.
Emotion metaphors in an awakening language
Authors: Amery Rob
Published: September 2021

Kaurna, the language of the Adelaide Plains, is an awakening language undergoing revival since 1989 (Amery 2016). Though little knowledge of Kaurna remains in the oral tradition and no sound recordings of the language as it was spoken in the nineteenth century exist, a surprising number and range of emotion terms were documented. A great many of these involve thetangka‘liver’ followed bykuntu‘chest’,wingku‘lungs’,yurni‘throat’ andyurlu‘forehead’, whilstmukamuka‘brain’ andyuri‘ear’ are involved in cognition. The role ofpultha‘heart’ is minimal. But these are not the only means to talk about emotions.Muiyu‘pit of the stomach’, a more elusive term, which may or may not be located in a body part andyitpi‘seed’ are also central to emotions. These three termstangka‘liver’,muiyu‘pit of the stomach’ andyitpi‘seed’, appear to be viewed byTeichelmann & Schürmann (1840)and especiallyTeichelmann (1857)as seats of emotion. In addition, there are a range of other means to express emotion, simple verbs and interjections.

This paper will discuss in detail the historical documentation, its interpretation and the ways in which this documentation is used today. In the context of re-introducing a reclaimed language, such as Kaurna, how to talk about emotions can become the topic of serious and sometimes unresolved debate. The title of a book of poetry (Proctor & Gale 1997) ended up having two translations, one involvingtangka‘liver’ and the otherpultha‘heart’. Historical phrases expressing emotions are often co-opted in names, speeches, poetry and written texts.
Relationship between 316L steel powder characteristics and residual stress in additive manufactured builds
Authors: Hodek J , Vavřík J , Brázda M
Published: September 2021

This investigation involved cube samples created by an Additive Manufacturing (AM) process. Four commercially available AISI 316L powders with a particle size range of 50-150 μm were used to produce four cube-shapes samples using Direct Energy Deposition (DED) in the industrial metal 3D printer InssTek MX-600. The contour method (CM), a destructive stress relaxation method, was used to determine the residual stress distribution on the cross-section. The results illustrate the impact of the powders on residual stress distribution after DED additive process.
Analysis of the relationship between changes in mechanical properties and precipitation in SUPER 304H steel during its exposure
Authors: Horváth J , Horváthová M , Pilsová L , Smola V , Chvostová E , Janovec J
Published: September 2021

Aim of the article is to provide properties comparison between initial state and two thermally exposed states of creep resistant steel SUPER 304H by usage of conventional and miniaturised tensile test specimens. Tests were performed at room temperature. Thermally exposed material was aged by 15 and 30 thousand hours at 675°C. This exposition which simulated accelerated operation exposition caused precipitation of intermetallic phases which affect mechanical properties like ultimate strength and elongation. The performed tests showed a decrease in elongation and ultimate strength between the first exposed state and initial state followed by partial increase of both tested values for the second exposed state. Sigma phase precipitation was confirmed for the exposed samples. The presence of the sigma phase also led to a change in the fracture morphology from full ductile (initial state) to combined ductile with the presence of brittle particle cleavage (exposed states). A comparison of the tests performed on classical and miniaturized test samples proved the possibilities of using miniaturized samples both for the basic material and for the exposed ones.
Material Properties of Steel with NiCr-Cold Spray Coating
Authors: Chocholousek M , Spirit Z , Brom J
Published: September 2021

The work is aimed on the NiCr-Cold spray coating applied on GOST 08CH18N10T steel and GOST 22K steel. Cold spray coating shows a high cohesion even as a few millimeter thick layer, therefore it has potential for the repairs not only of the energy industry components. Applied on the steel substrate, the cold spray can be considered as a bimetallic material for the purpose of the mechanical properties evaluation. Performed comparison based on tensile mechanical properties at room temperature and at 350 °C of separate steels and cold spray versus bimetallic combination is discussed. The main goal is to find the optimal approach of bimetallic material evaluation. Additional metallographic and microstructural analysis is attached to show the differences between the used combinations. Influence of possible heat treatment on the mechanical and adhesive properties is also included.
Mechanical Behaviour of Type 316L Austenitic Stainless Steel in Low Pressure Hydrogen Steam Environment
Authors: Janoušek J
Published: September 2021

Low pressure superheated H2-steam appears to be an interesting alternative to pressurized water environments, since it is capable of performing accelerated environmentally assisted cracking (EAC) experiments for nickel base and stainless steel alloys. Constant Extension Rate Tensile (CERT) tests were performed with strain rates of 2 × 10−6 or 2 × 10−8 ms−1 at 350, 400, 440 and 480 °C on flat tapered specimens of Type 316L austenitic stainless steel. The tapered shape allows the determination of crack initiation over a range of stresses and strains simultaneously on one specimen and therefore the threshold stress value was obtained. The environment was 6 times more oxidizing than the dissociation pressure of NiO. The acquired mechanical properties are summarized and threshold stresses for EAC crack initiation are evaluated.
Design & Modelling of Double Cantilever structure by Stainless Steel 316L deposited using Additive Manufacturing Directed Energy Deposition Process
Authors: Kiran A , Hodek J , Vavřík J , Brázda M , Urbánek M , Cejpek J
Published: September 2021

Distortion in the metal additive manufacturing due to inherent residual stress during the separation of the deposited part from the base plate is critical. Distortion gets amplified after removing it from the build platform. Internal stress in the deposited sample during the material deposition and cooling phase is crucial to estimate. Residual stress in the structure influences structural distortion. Numerical analysis of residual stress prior to deposition helps to identify inconsistent stress in the built part and helps to take required measures like optimising process parameters, base plate preheat to make it less significant. Residual stress estimation before deposition using numerical calculation plays a major role in the improvement of the built part and establishing technology for a wide application. A numerical model for thermal history and residual stress estimation has been developed for Directed Energy Deposition (DED). A standard double cantilever model was considered for physical deposition and numerical model verification. Thermal history from Finite Element (FE) Analysis was compared with the in-situ measurement. A close agreement was noticed between in situ measurement and simulation results. A double cantilever was built using austenite stainless steel 316L by the DED technique. Internal stress in the deposited part before and after a partial separation from the base plate was compared. Numerical results comparison before and after separation emphasize the impact of residual stress on distortion.
New approach to heat treatment of spring steel
Authors: Kotous J , Salvetr P , Procházka R
Published: September 2021

In the 54SiCr6 spring steel, a spheroidized structure was achieved by two processing methods: conventional soft annealing above the temperature A1 in a furnace and accelerated ASR annealing by an induction heating equipment. The ASR technology is much faster, even for materials with a worse tendency to the spheroidisation, such as steels with higher silicon content. Thanks to this, a finer structure is obtained. This is the basis of other advantages for the subsequent hardening. Quenching can be done at lower temperatures, higher yield and tensile strength is obtained while maintaining same or improved ductility and contraction. This also results in influencing of fatigue behavior.
Influence of surface structures on wettability
Authors: Kvitek L , Saran D , Vaclavek L , Kapusta J , Kozmin P
Published: September 2021

Wettability of solid surfaces is a key parameter for many industrial applications of solid materials. The wettability is influenced not only by the nature of the material but also by the existence of surface structures. Crucial influence of the oriented surface structures on the shape of liquid drop was observed in this study. Observed differences in value of contact angle measured on the metal surface at two perpendicular directions were 19° for water and 23° for diiodomethane. These surface structures can significantly influence liquid and heat transfer on structured surfaces.
Theoretical study of the process of balls rolling with a diameter of 40 mm on a ball rolling mill
Authors: Naizabekov A , Mukhametkaliyev B , Lezhnev S , Panin E
Published: September 2021

The following calibration scheme for rolling round steel is used for producing thermally hardened grinding balls with a diameter of 40 mm at JSC SSGPO for 320 variety rolling mill: a round billet with a diameter of 40 mm is produced from the initial billet of 120 × 120 mm. In the last developed scheme the square billet 150x150 mm is used as an initial billet for whole mill where the round steel with diameter of 40 mm is obtained from the above mentioned billet and then this round steel is used for production of balls with a diameter of 40 mm. Computer simulation of the ball rolling process in the Simufact Forming program was performed. The results of strain state distribution showed that the maximum processing level in the surface layers of balls is observed, while the stress state distribution showed that in the surface layers prevail high compressive stresses up to −400 MPa. Such stress-strain state leads to formation of gradient structure in the ball cross-section, where the surface layers will have more high mechanical properties. That is the most optimal result for details worked in condition of high values of friction.
Characterization of Microstructure Variations by Laser-Ultrasound during and after the Heat Treatment of Metals
Authors: Scherleitner E , Kerschbaummayr C , Haderer W , Reitinger B , Mitter T , Gruensteidl C
Published: September 2021

We demonstrate the potential of laser ultrasound for non-destructive testing applications in steel production and processing in two use cases: (1) Imaging of the grain structure transition between the thermally hardened surface and the unaffected core material with a comparison to sectional views by an optical microscope. We found very good correlation between the laser ultrasonic image and the microscopic view at the cross section. (2) In situ monitoring of Poisson’s ratio of steel sheets during thermal processes by evaluation of resonant frequencies of Lamb waves. In our ongoing research the results will be correlated to metallurgical properties of interest.
Influence of micro- and nanoparticles on mechanical properties of magnesium and magnesium alloys
Authors: Trojanová Z , Lukáč P , Džugan J
Published: September 2021

Magnesium and magnesium alloys were reinforced with various micro- and nanoparticles (SiC, Inconel718, AI2O3, ZrC2, BN, graphite) Composites were prepared by squeeze casting and using powder metallurgy followed by hot extrusion. Tensile and compression tests were performed at elevated temperatures up to 300 °C. The influence of micro- and nanoparticles on mechanical characteristics is discussed on the base of physical models. Bonding at the interface between particles and magnesium matrix plays an important role for the resulting composite properties.
Determination of Fracture Limit Line in Principal Strain Space by Shear Tests
Authors: Urbánek M. , Fedorko M. , Rund M.
Published: September 2021

The main goal of this paper was to define a new limit line, which expands Forming Limit Curve (FLC) more precisely Fracture Forming Limit Curve (FFLC). The new limit line was defined by damage models transformed from triaxiality-fracture strain space to the major/minor strain space and we focused on the shear area. Because FLC and FFLC have some limitations, for example, some Advanced High Strength Steels (AHSS) fractures before thinning. Another limitation can be seen on the left side of the diagrams in the shear region, where the part can break in the process without crossing the FLC or FFLC. The different shapes of samples were used for finding a new line of the FFLC and Deep Drawing Test (DDT) was used for verification. The fracture points from measurement were used for calibration of simple uncoupled damage models. The simple model means model, which is calibrated based on one or two measurements (tensile test or tensile test + shear test). This paper was used an Advanced High Strength Steel (AHSS) DP1000 sheet with a thickness of 0.8 mm for the experiments.
Possibilities of using thermally sprayed coatings for surface treatment of rail vehicles components
Authors: Vostřák M , Brodský J , Houdková Š , Šulcová P
Published: September 2021

Thanks to their versatile properties and economical applicability, thermally sprayed coatings are being used in more and more areas of industry. Within the research project, suitable alternatives are being sought for the replacement of surface treatments of selected components of rail vehicles with thermal spraying. The aim is to increase the functionality and service life of selected parts and thus the entire vehicle. Based on the requirements for the functional properties of components, variants for the material and technology of thermal spraying are selected. Technologies considered include HVOF, TWAS, FS, and APS, materials include Fe, Ni, Zn, and Mo based alloys; WC and CrC based cermets. The basic functional properties of these coatings are analyzed and discussed. The further steps of the work to test suitability of these coatings for selected applications and are outlined.
Corrosion behaviour of hydroxyapatite (HAP) coated AISI 316Ti austenitic biomaterial
Authors: Zatkalíková V , Markovičová L , Uhríčik M , Hanusová P
Published: September 2021

HAP bioactive coatings are widely applied to improve the bone response in orthopedic and dental stainless steels implants. Mechanical properties of the metallic implant are preserved and moreover, HAP improves the corrosion resistance. This article deals with the corrosion resistance of AISI 316Ti austenitic biomaterial with electrochemically deposited HAP coating. Corrosion behaviour is evaluated on the bases of two independent methods-the electrochemical potentiodynamic polarization test and exposure immersion tests, both carried out in physiological solution (0.9 % NaCl) at the temperature 37 ± 0.5 °C. The microstructure and chemical composition of HAP coating is evaluated by SEM and EDX analysis. According to the results of the potentiodynamic test, the HAP coated biomaterial shows the considerably higher corrosion resistance compared to that without the HAP coating. However, the corrosion losses and SEM analysis after the exposure test revealed severe disruption of the HAP coating and the stainless steel substrate started to corrode.
Higher Stickelberger ideals and even 𝐾-groups
Authors: El Boukhari Saad
Published: September 2021

We use the analogy between class groups and even

K
K

-groups of the ring of integers of a number field and “Higher Stickelberger” ideals within

K
K

-theory to prove an index formula for these ideals in a finite abelian extension of real number fields, which is similar to the classic Stickelberger ideal index formula proved by Iwasawa.
On the existence of foliations by solutions to the exterior Dirichlet problem for the minimal surface equation
Authors: Aiolfi Ari , Bustos Daniel , Ripoll Jaime
Published: September 2021

Given an exterior domainΩ\OmegawithC2,αC^{2,\alpha }boundary inRn\mathbb {R}^{n},n≥3n\geq 3, we obtain a11-parameter familyuγ∈C∞(Ω)u_{\gamma }\in C^{\infty }\left ( \Omega \right ),|γ|≤π/2\left \vert \gamma \right \vert \leq \pi /2, of solutions of the minimal surface equation such that, if|γ|>π/2\left \vert \gamma \right \vert >\pi /2,<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="u Subscript gamma Baseline element-of upper C Superscript normal infinity Baseline left-parenthesis normal upper Omega right-parenthesis intersection upper C Superscript 2 comma alpha Baseline left-parenthesis normal upper Omega overbar right-parenthesis">uγ∈C∞(Ω)∩C2,α(Ω¯)u_{\gamma }\in C^{\infty }\left ( \Omega \right ) \cap C^{2,\alpha }\left ( \overline {\Omega }\right ),uγ|∂Ω=0u_{\gamma }|_{\partial \Omega }=0withmax∂Ω‖∇uγ‖=tan⁡γ\max _{\partial \Omega }\left \Vert \nabla u_{\gamma }\right \Vert =\tan \gammaand, if|γ|=π/2\left \vert \gamma \right \vert =\pi /2, the graph ofuγu_{\gamma }is contained in aC1,1C^{1,1}manifoldMγ⊂Ω¯×RM_{\gamma }\subset \overline {\Omega }\times \mathbb {R}with∂Mγ=∂Ω\partial M_{\gamma }=\partial \Omega. Each of these functions is bounded and asymptotic to a constant\[cγ=lim‖x‖→∞uγ(x).c_{\gamma }=\lim _{\left \Vert x\right \Vert \rightarrow \infty }u_{\gamma }\left ( x\right ) .\]The mappingsγ→uγ(x)\gamma \rightarrow u_{\gamma }\left ( x\right )(for fixedx∈Ωx\in \Omega) andγ→cγ\gamma \rightarrow c_{\gamma }are strictly increasing and bounded. The graphs of these functions foliate the open subset ofRn+1\mathbb {R}^{n+1}\[<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="left-brace left-parenthesis x comma z right-parenthesis element-of normal upper Omega times double-struck upper R comma minus u Subscript pi slash 2 Baseline left-parenthesis x right-parenthesis greater-than z greater-than u Subscript pi slash 2 Baseline left-parenthesis x right-parenthesis right-brace period">{(x,z)∈Ω×R, −uπ/2(x)>z>uπ/2(x)}.\left \{ \left ( x,z\right ) \in \Omega \times \mathbb {R}\text {, }-u_{\pi /2}\left ( x\right ) >z>u_{\pi /2}\left ( x\right ) \right \} .\]Moreover, ifRn∖Ω\mathbb {R}^{n}\backslash \Omegasatisfies the interior sphere condition of maximal radiusρ\rhoand if∂Ω\partial \Omegais contained in a ball of minimal radiusϱ\varrho, then\[[0,σnρ]⊂[0,cπ/2]⊂[0,σnϱ],\left [ 0,\sigma _{n}\rho \right ] \subset \left [ 0,c_{\pi /2}\right ] \subset \left [ 0,\sigma _{n}\varrho \right ] ,\]where\[σn=∫1∞dtt2(n−1)−1.\sigma _{n}=\int _{1}^{\infty }\frac {dt}{\sqrt {t^{2\left ( n-1\right ) }-1}}.\]One of the above inclusions is an equality if and only ifρ=ϱ\rho =\varrho,Ω\Omegais the exterior of a ball of radiusρ\rhoand the solutions are radial.

These foliations were studied by E. Kuwert in [Ann. Inst. H. Poincaré Anal. Non Linéaire 10 (1993), pp. 445–451] and our result answers a natural question about the existence of such foliations which was not touched by Kuwert.
In Search of an Honest Butterfly: Sexually Selected Wing Coloration and Reproductive Traits From Wild Populations of the Cabbage White Butterfly
Authors: Espeset Anne E , Forister Matthew L
Published: September 2021

Sexual selection is central to many theories on mate selection and individual behavior. Relatively little is known, however, about the impacts that human-induced rapid environmental change are having on secondary sexually selected characteristics. Honest signals function as an indicator of mate quality when there are differences in nutrient acquisition and are thus potentially sensitive to anthropogenically altered nutrient inputs. We used the cabbage white butterfly, Pieris rapae (L.) (Lepidoptera: Pieridae), to investigate differences in color and testes size in a system that is often exposed to agricultural landscapes with nitrogen addition. We collected individuals from four sites in California and Nevada to investigate variation in key traits and the possibility that any relationship between wing color and a reproductive trait (testes size) could vary among locations in the focal butterfly. Coloration variables and testes size were positively albeit weakly associated across sites, consistent with the hypothesis that females could use nitrogen-based coloration in the cabbage white as an indicator for a male mating trait that has the potential to confer elevated mating success in progeny. However, variation in testes size and in the relationship between testes size and wing color suggest complexities that need exploration, including the possibility that the signal is not of equal value in all populations. Thus these results advance our understanding of complex relationships among environmental change and sexual selection in the wild.