bluuebunny/crossref_metadata_2025 huggingface dataset:
“Emergency Distance Education” Model: How Normal Could The Projected New Normal Be?
Authors: Borokhovski Eugene , Pickup David , Tamim Rana
Published: May 2021

In this opinion piece, the authors critically consider the transition to the ‘emergency model’ of distance education (DE), forced by the pandemic and associated restrictions to our daily life, paying special attention to its potential pitfalls. The authors argue in favour of more careful approach to DE design and implementation over the ‘one size fits all’ solution. The data from previous meta-analyses in the field of DE and technology integration in education are briefly summarized to provide research-based support for the following observations: (1) students’ academic achievements in DE are largely associated with the interactivity factor, which is also instrumental in preventing excessive drop-out rates; (2) the flexibility factor that largely predetermined the initial rise and rapid proliferation of DE should be maintained to avoid negative side-effects, including student’ dissatisfaction and drop-out; (3) pedagogical factors, imbedded in careful instructional design, outweigh technological affordances, especially since the latter require properly organized and managed infrastructure, adequate training for teachers an students, and sufficient time to be efficiently adopted in formal education to reveal its potential for successful teaching and learning; (4) vast variability of meta-analytical findings, even with the most favourable to DE average point estimates, do not only present educational system with pleasing promises, but also call for serious caution as the negative effect sizes are almost equally prevalent as the positive ones. In conclusion, the paper reminds educational practitioners and policy makers: what comes to life out of necessity does not necessarily present viable solutions in the long run.
Digital Technologies in the Training of Psychologists in Vladivostok
Authors: Gerasimova Irina
Published: May 2021

In the context of the information volumes continuous growth, the digitalization of education is considered a necessary tool for the modernization of the educational system. There is a pronounced specificity of training specialists in the various fields of science - natural, humanitarian, technical and exact. How does work differ in the different forms of training specialists - full-time and part-time. There are peculiarities, opportunities and traditions in every particular university. In this regard, the problem arises of the need to digitalize education, determining the measure, and sufficiency in each case. The functioning of the current digital educational environment is due to both the psychophysiological capabilities of the human body, moral and ethical principles. The purpose of the study is to identify the saturation of digital educational technologies in the process of full-time training of students-psychologists and conflictologists at FEFU. Research methods: problematization, survey, observation. The author examines two components of digitalization at the university - the learning process, and its organization and concludes the sufficiency of the information technologies use in the training of psychologists and conflictologists at FEFU. The author also draws attention to the active use of technical means in the educational process - the formalization of education, which manifests itself in a decrease of students’ motivation, loss of interest, involvement, “non-appropriation” of information. Prevents direct transfer of distance learning formats to full-time. Requests the need for informational support of teachers. Emphasizes attention to ensuring the high-quality functioning of technical means.
Readiness for the Profession of Students With Different Psychotypes in a Digital Educational Environment
Authors: Zholudeva Svetlana , Zhukova Rufia , Naumenko Marina
Published: May 2021

In this article, the authors examined the readiness for the profession of students with different psychotypes studying in a pedagogical direction in a digital educational environment. The purpose of this study is to study the readiness for the profession of students with different psychotypes, studying in a pedagogical direction in a digital educational environment. The article deals with the classification of personality psychotypes. The main theoretical approaches to the concept of readiness for the future profession of students are analyzed. Studied the readiness for the profession of students with different psychotypes in the digital educational environment. The study involved 60 respondents - students of the pedagogical direction of the Southern Federal University. The research methods were psychodiagnostic techniques and methods of mathematical statistics. The data obtained as a result of the research will help to select a new or change the existing toolkit for working with students in the process of forming their professional competencies and skills, as well as make adjustments to the content and methods of providing the main and additional educational material in the framework of the digitalization of the educational sphere of activity.
Organization of safe execution of works with the use of trapping nets
Authors: Brodskiy Victor
Published: May 2021

The organization of ensuring safe execution of building and assembly works when erecting and reconstructing buildings (structures) of various purposes based on the application of trapping nets to prevent industrial injuries in case of human or items falling from height is presented. Structural layout of a safety (catching) device with pivotally mounted brackets and a freely hanging net was considered. Appearing dynamic loads in case of items falling on trapping nets depending on impact acceleration were theoretically identified. It was found out that a trapping net with pivotally positioned brackets additionally reduces deceleration loads in relation to devices with rigidly fixed brackets and their use is more effective for cases of men falling with insignificant forward velocity. Bench and shop tests of trapping devices were carried out with the purpose of checking compliance of selected theoretical models, selection of developed options of designs and schematic diagrams, differentiation of reaction of capron and lavsan net materials from action of impulse loads. Test key results confirming matching of experimental data with presented theoretical models were showed. It was established that dynamic overloads depend both on a bracket position angle as well as on a place of an item falling into net, the value of pitch of deflection of net cloth made of lavsan and capron materials is almost similar and characteristics of values of their displacement under dynamic loads from a falling item are identical.
Organizational-and-technological solutions for installation of prefabricated roof coverings from roll materials
Authors: Zhadanovsky Boris , Sinenko Sergey , Mirzakhanova Aida
Published: May 2021

Implementing the modern technological methods is recommended in the article, as well as performing some operations. It should be considered that small and medium-sized enterprises involved in the construction of industrial and civil facilities are also installing the roof coverings. The algorithm of technological operations is as follows: preparatory work; gluing a two-layer waterproofing roofing on freshly formed reinforced concrete panels; double rolling of the uncooled roll roofing after removing the panel from the steam chamber. The process of installing the waterproofing roofing has to be carried out in a specially equipped enterprise area. It is recommended to use the following domestic and foreign tools and equipment for above-mentioned operations. Such equipment is a truck crane (for example, KS-45717), a roof crane (KL-3), a temporary fence, a metal ruler, a tape measure, roller or a brush, a scraper, a roofing knife and a roller (weight is 100 kg).The rational methods of roofing installation (based on labor intensity) are presented. As was substantiated, the calculation of labor can change while improving the technology and the tools and equipment used. The quality control of operations is described, it involves visual inspections and the necessary measurements performed with a ruler. Optimal organizational and technological solutions, which allow to manage processes taking into account the safety of workers, were obtained. Fulfilling the labor safety requirements during construction (part 1 and part 11) is primary while installing the roll-up waterproofing roofing made of melting roofing material with the help of a solvent. In addition, it should be noted that the workplaces and storage locations with flammable materials and substances have to be provided with a portable fire stand, as well as with fire extinguishing and medical equipment. The conclusions and recommendations on organizational and technological solutions forin stalling the prefabricated roofing from roll materials by using mechanization means are presented. They are intended for developers of organizational and technological documentation, including flow charts, work projects, regulations, codes of rules. They will be useful for students, masters, graduate students studying for professions related to the production of building, erection and special works.
Application of the method of complex assessment of the quality of high rise apartment buildings in practice
Authors: Shesterikova Yana
Published: May 2021

A comprehensive approach to the problem of improving the quality of construction of residential buildings, allows you to take into account various main factors that affect the quality of construction in General. Using the method of expert opinions, the most significant parameters were identified. The weight of each factor is determined using a mathematical model. The experiment examined three levels of variation in significance for each group of factors. After obtaining a discrete value of a complex indicator of the quality of construction of a residential building, it is interpreted using adapted quantitative ranges of values of the generalized Harrington desirability function. A method has been developed to determine the effectiveness of organizational and technological decisions made. An algorithm has also been developed to improve the quality of residential building construction.
Increasing of effectivity of construction project on account of integration of information technologies
Authors: Govorukha Petr
Published: May 2021

A conceptual methodology for increasing the efficiency of organizational and technological aspects of construction production by developing a predictive tool for participants in a construction project is described here. The initial direction of activity for working off the possibility of implementing the indicated methodology has been determined. During the analysis of a domestic experience of construction companies, the conditions for unlimited and constant integration of information technology (IT) were identified. The importance of constant tracking of innovations in the field of information technology for the selection of the most promising areas and methods of their integration, allowing the participants in a construction project to increase their efficiency at the lowest cost, was found. The description of the principles of systems engineering for the development of monitoring models in the field of IT is brought. The primary classification of information technologies from the point of view of the application in the construction industry is carried out. Based on consultations held with the leaders of construction companies there were defined the groups and subgroups of parameters, that may influence the effectiveness of realization of the construction project.
Toward the formation of parameters influencing the quality of low-rise residential buildings
Authors: Lapidus Azary , Ndayiragije Yves , Stepanov Alexander
Published: May 2021

The construction industry occupies a significant place in the development of any country. The success level of construction projects largely depends on its quality. Poor performance of work leads to different losses. Effective quality management delivers customer satisfaction and value, reduces visible and less visible cost of poor quality. The article aims to identify the main parameters influencing the quality of low-rise residential buildings using expert opinion method. At the first stage, a literature review was conducted, which resulted in a list of 54 individual indicators of technical solutions that affect the quality of low-rise apartment buildings. These quality indicators have different degrees of influence. Experts identified indicators that have a greater impact on the comprehensive quality indicator. Then, the list was shortened up to 34 individual indicators. The survey was conducted in construction companies, research centers, and construction universities. The development of a comprehensive quality index contributes to the achievement of design decisions in construction of residential buildings. The methodological scheme of the study is shown. Using the method of exploratory factor analysis, all indicators were grouped into 7 groups. A conceptual measurement model is defined. Furthermore, a structural model to determine the influence weights of each individual indicator on the corresponding group of factors is shown.
Assessment of organizational and technological reliability of a construction organization during contract bidding
Authors: Mikhaylova Elena
Published: May 2021

In the current system of contract bidding, there are a number of problems, one of which is the imperfection of the evaluation criteria by which applicants are selected. The article presents a methodology for assessing the organizational and technological reliability of a construction organization and its competitive offers for tenders for construction and installation works. It is proposed to use the indicator of its organizational and technological reliability as a criterion for evaluating a construction organization that claims to fulfill a construction order. To determine the reliability of a construction company, information about the intensity of development of capital investments is used. This indicator allows you to assess how much the bidder can ensure the maximum return on the construction equipment and workers used, reduce the cost of construction using modern construction materials and resource-saving technologies. Each construction and installation organization will have its own intensity of development of capital investments. It depends on the qualification of employees, the availability and use of a fleet of construction machines and mechanisms, construction production technologies, construction organization methods, etc. As an indicator that characterizes the relative change in the actual development of capital investments from the standard or calculated value, the capital investment development index is used. Using retrospective data on the speed of capital investment development for similar objects or using variant design of the construction process, curves of accumulated probabilities of capital investment development indices are constructed, which are used to determine the organizational and technological reliability of the contract bidder. The proposed assessment of the reliability of a construction organization allows the customer (investor) to choose a reliable partner – contractor that best meets their requirements.
Asymptotic approximation of the solution of a perturbed differential equation system
Authors: Petelina Vera
Published: May 2021

The article is devoted to the determination of second-order perturbations in rectangular coordinates and components of the body motion to be under study. The main difficulty in solving this problem was the choice of a system of differential equations of perturbed motion, the coefficients of the projections of the perturbing acceleration are entire functions with respect to the independent regularizing variable. This circumstance allows constructing a unified algorithm for determining perturbations of the second and higher order in the form of finite polynomials with respect to some regularizing variables that are selected at each stage of approximation. Special points are used to reduce the degree of approximating polynomials, as well as to choose regularizing variables. The problem of generation of an asymptotic approximation of the solution of a perturbed differential equation system is considered in the case where a bifurcation occurs in the “fast motions” equation when the parameter changes: two equilibrium positions merge, followed by a change in stability.
Temperature distribution in an elliptical body with an internal heat source with partial adiabatic isolation
Authors: Kanareykin Alexandr
Published: May 2021

The article calculates the temperature field in an elliptical body with internal heat dissipation. In this case, the boundary conditions are boundary conditions of the third kind. The solution is located at the transition to the elliptic coordinate system. The author has obtained an analytical solution for the distribution of the temperature field in a body with an elliptical cross-section of infinite length with zero ambient temperature with partial adiabatic isolation in the form of a functional series using hypergeometric functions.
Informatization of teaching based on interdisciplinary connections of robotics with other subjects
Authors: Yermekova Zhadyra , Stukalenko Nina , Kozhabekova Elmira , Magauova Akmaral , Sapargali Pazylbek , Sadvakassova Zukhra
Published: May 2021

In this work, the results of a study regarding the methodological aspects of organizing training courses in robotics in a school educational process are presented. In the course of the study, an analysis of the problem was carried out and the conditions for the effective implementation of teaching robotics to students of a comprehensive school based on developing educational technologies, integration processes and interdisciplinary communications were identified. The process of development of the cognitive interests of students in robotics was investigated in one of the specialized lyceum of the Capital city of Kazakhstan. Based on the results of the study, the theoretical foundations of the process under study are summarized, the prerequisites for updating the problem are established, and the scientific and methodological aspects of teaching robotics in the conditions of the school educational process are considered. The results obtained are of theoretical and practical importance for modern education, the implementation of the leading ideas of educational informatization.
Human capital in an industrial impasse
Authors: Ibragimov Radiy
Published: May 2021

Crises, shaking developed economic systems, force us to look for strategic ways of development, alternative to the usual paradigm, in which the main vector of development from a pre-industrial to a post-industrial economy leads to a global model of a consumer society, beyond which there is a social abyss. The latest shock to the global economic system is the COVID-19 pandemic. To overcome this misfortune, authoritative experts propose a series of radical organizational and economic measures, but their goal is old - to preserve consumption as the main economic motive of social behavior. This, in turn, leaves in force the global civilizational risks and preserves the status of a myth for the concept of «sustainable development». The proposed article contains an attempt to substantiate an alternative vision of the model of history, in which it is proposed to consider the pre-industrial type of economy as basic on the basis of such criteria as efficiency, prospects and adequacy of the reproduction of human capital. Finally, sustainable development of a socio-economic system of any scale is possible only if such antagonistic indicators as production efficiency and employment of the population are reconciled. And this is possible only in a pre-industrial type of economy.
The higher education system as the driving force of the country’s sustainable development
Authors: Vlasov Maxim
Published: May 2021

The article presents results of the research on patterns of the influence such factors as mass character, internationalization and state financing of higher education have on country’s innovation development parameters. Conducting correlation analysis allowed for obtaining academic proofs of the fact that in modern conditions above mentioned characteristics of higher education system define innovation development of the country in general. The first part of the article contains analytical review of the literature and identifies characteristics of higher education system the influence of which on country’s innovation development the authors consider as significant (mass character, internationalization, state financing). The second part describes the methodology of research and formulated working hypotheses. The third part is a presentation of obtained research results, whereas the fourth part contains conclusions. Theoretical importance of the conducted research is in defining patterns in which such higher education system characteristics as mass character, internationalization and financing model influence certain parameters of innovation development, in particular, the share of hi-tech export in the overall amount of industrial export and the share of research and development costs in GDP.
Optimization algorithms in the design of switched-reluctance machines
Authors: Shevkunova Anastasia V.
Published: May 2021

Currently, the level of industrial development is determined by the intellectual capacity of the equipment used. To increase the energy efficiency of production in various industries, it is necessary to introduce automated electric drives based on promising switched-reluctance motors. The geometric parameters of the active part of the switched-reluctance motor were calculated. As a criterion, the maximum value of the average value of the electromagnetic moment for the switching period was taken as the basis. Optimal design was carried out by means of the computer-aided design program developed by the author in co-authorship. It, in turn, includes optimization algorithms based on stochastic and deterministic methods. The developed program for optimizing the active part of the switched-reluctance motor was implemented using the Matlab application software package, which directly interacts with the FEMM program for calculating and visualizing electromagnetic processes. Finding the most energy-efficient engine geometry was performed in two stages, in order to determine the geometric parameters of the engine tooth zone that have a dominant influence on the value of the electromagnetic moment, as well as to ensure a guaranteed finding of the global extremum of the target function.
New principles of heat recovery of ventilation emissions from multi-apartment buildings (AB)
Authors: Vasilyev Gregory , Timofeev Nikolay , Kolesova Marina , Yurchenko Igor , Marchenkova Svetlana , Dmitriev Alexander
Published: May 2021

The article shows results of studies on assessing the effectiveness of new principles for heat recovery of exhaust air in ventilation systems of apartment buildings (AB). Technological solutions are known that provide heat recovery of the exhaust air for heating the supply air of ventilation systems. The efficiency of such solutions can reach 90%, but only in the coldest five-day period of the year with the maximum temperature difference between the exhaust and supply air. At all other times of the heating season, the efficiency of the recuperative heat exchangers decreases as the outside air temperature rises. In the studies presented in the article, a technology was considered that was free from this drawback. It is based on a two-stage heat recovery of the exhaust air: first, recovery for heating the supply air, and then “additional recovery” using heat pumps for the needs of AB hot water supply. The article shows results of assessing the effectiveness of the proposed two-stage heat recovery of exhaust air in various regions of the Russian Federation.
Integrated strategic model for managing regional projects in the field of ecology
Authors: Shedko Yuri , Alenteva Nadezhda , Anokhin Sergey , Lukiyanova Marina , Starovoitov Vladimir
Published: May 2021

The article is devoted to review of authors’ model of project management while executing the strategy of sustainable regional development. The article analyses the essence of social partnership as a collaborative instrument between government, business and society, which influences on economic progress nowadays. It is concluded that improvement of relations between actors of cooperation depends on institutional framework formation as well as on effective methods of management. In this paper there is defined such a condition of economic development as technological progress, which results in resources accumulation in developed regions but intensifies the problem of regional socio-economic inequality. There is proposed and proved the model of cooperation between society and government during implementation the strategy of regional development taking into account the digitalization. Thus resistance of the strategy depends on dimension of project agreement. In this context it becomes important to include into the strategy such a factor as trust. It should be noted that in the article there are defined organization opportunities, which have to be applied during strategic planning of the project to secure sustainable competitive position of the region and business entities. There are also described the reasons for resisting of project management adoption.
Region innovative development in the Russian economy technological transformation: ecosystem approach
Authors: Salamatov Artem , Maltsev Yuriy , Pavlov Nikita
Published: May 2021

The article considers the ecosystem approach to regional development. The ecosystem approach allows under conditions of technological transformation of the economy to maintain the socio-ecological-economic balance of the region, to develop the culture and quality of life of the region's population. The structure of ecosystem of the region, the main actors of which are the actors of the system, is considered. By ecosystem we understand a self-organizing, highly adaptive, territorially limited within the natural, institutional, social and political environment network complex of freely cooperating, interacting and mutually influencing each other actors - organizations, processes, projects, services. The core of ecosystems are firms where the first business model prevails and network effects are evident. Russia is in the process of realizing the importance of the ecosystem approach to regional development in the context of technological transformation of the economy. Further development consists in the introduction of "green growth" of the economy, where it is impossible to do without taking into account the ecosystem effects, the development of comprehensive programs for the development of the territory based on the principles of sustainable development.
Dual approach to the assessment of the project management system performance and the results of its application in the ITER Project
Authors: Morozenko Andrey , Zyablov Alexey , Gorshkov Andrey , Shvets Natalia , Byzov Vladimir
Published: May 2021

The article considers the current problem of low efficiency of tools and methods used to assess the project management systems of complex engineering facilities. The problem is important today because engineering companies strive to increase their rating in a highly competitive market, and this issue is of a special concern in the international market of goods, works and services. The article presents the methodology for the assessment of the project management system, based on the simultaneous cross-section use of approaches to the assessment of project management and personnel management processes (the so-called “processes – personnel” pair) with the use of questionnaire-dialog forms of data collection. The essence of the study was to search for patterns of cross-assessment results, their comparison and determination of algorithms of mutual influence on each other, and what is necessary for a more accurate assessment of the management system. The scientific novelty of the research is the development of a set of interrelated indicators of the management system behavior in a company. The presented method was tested by the team of authors of this article during the management assessment of the international project on the construction of a thermonuclear reactor (ITER, France) in 2020. The results of the study revealed the comparability of the assessment results, confirmed the impact of the assessment results on each other and determined the possibility of predicting the assessment results per individual indicators, depending on the state of the management system in the “process-personnel” pair. This method can be used to assess the management systems of any project-oriented companies implementing capital construction projects. In the future, it can become the basis for creating a specialized standard for assessing the construction project management systems.
Achieving sustainability and environmental enhancements through a “collaboration toolkit” to deliver new sustainability strategies for The Emirate of Ajman − UAE
Authors: Challender Jason
Published: May 2021

Governments are faced with ever challenging dilemmas to find practical sustainable solutions and proposals for some scientific and problems around adopting clean sustainable energy whilst reducing waste. This is certainly an issue for Ajman which has been heavily dependent on fossil fuels for energy and had a detrimental and adverse effect on its environmental sustainability credentials in the past. This paper focuses on the use of a “collaboration toolkit” has been developed by the author and which is currently being piloted in the UK on a live project. The sole purpose of the toolkit is to deliver improved environmental sustainability solutions on construction and engineering projects. The toolkit will provide a holistic and joined up approach across the supply chain to meet the demands of the carbon neutral agenda. This will entail reducing embodied carbon in buildings, collaboration with energy partners to assess ways and means of reducing gas, electricity and water consumption and reviewing appropriate renewable technologies. It is hoped that the toolkit can prove beneficial for Ajman in overseeing a new environmental sustainability strategy for its construction and engineering projects and therein contributing to overall social, environmental and economic impacts.
Leiomyosarkom der Vena saphena magna – der seltene Fall
Authors: Köpnick Sven , Traska Thilo , Golz Reinhard
Published: May 2021

Wir berichten über eine bisher gesunde 58-jährige Patientin, die sich mit stärksten persistierenden lokalen Schmerzen am distalen medialen Oberschenkel rechts in unserer Klinik vorstellte. Begleitsymptome wie lokale Schwellung oder Rötung lagen nicht vor. Sonografisch zeigte die Vena saphena magna im angegebenen Schmerzbereich am distalen Oberschenkel eine suspekte isolierte Ektasie mit einer umschriebenen echoarmen, solid erscheinenden Gefäßwandläsion bei sonst im übrigen Gefäßverlauf unauffälligem Sonografiebefund.

Nach operativer Resektion wurde die Diagnose eines mäßig differenzierten vaskulären Leiomyosarkoms gestellt.

Weichteilsarkome sind verglichen mit anderen Tumorerkrankungen sehr selten.

Das venöse Leiomyosarkom betrifft bevorzugt die Vena cava inferior, sehr selten die Vena saphena magna. Für die Prognose ist eine frühzeitige Diagnose entscheidend. Häufig liegt bei Diagnosestellung bereits eine Metastasierung mit entsprechend ungünstiger Prognose vor.

Bei unklaren Symptomen und Sonografiebefunden im Bereich des Gefäßsystems sollte, trotz seltenen Vorkommens, auch an eine neoplastische Erkrankung gedacht werden.
α-Xanthylmethyl Ketones from α-Diazo ketones
Authors: Miranda Luis D. , López-Mendoza Pedro
Published: May 2021

A simple and efficient method to obtain α-xanthylmethyl ketones from α-diazo ketones is described. The reaction proceeds through a protonation/nucleophilic substitution sequence in the presence of p-toluenesulfonic acid and potassium ethyl xanthogenate as the nucleophile. As α-diazo ketones can be readily synthesized from ubiquitous carboxylic acids, a broad variety of xanthates can be obtained, including examples from naturally occurring substrates.
Radioembolization for Rare Metastatic Disease
Authors: Niekamp Andrew S. , Narayanan Govindarajan , Schiro Brian J. , Pena Constantino , Powell Alex , Gandhi Ripal T.
Published: May 2021

Radioembolization has become a widespread treatment modality for both primary and metastatic hepatic malignancies. Although the majority of data and indication for yttrium-90 radioembolization have been for hepatocellular carcinoma and metastatic colorectal cancer, radioembolization with yttrium-90 has rapidly expanded into the treatment options for multiple tumor types with metastases to the liver. This article reviews the clinical data and expanding utilization of radioembolization for rare metastatic diseases with an emphasis on efficacy and safety.
Modulation-slippage trade-off in resonant four-wave upconversion
Authors: Griffith A. , Qu K. , Fisch N. J.
Published: May 2021

Following up on a proposal to use four-wave mixing in an underdense plasma at mildly relativistic laser intensities to produce vastly more energetic x-ray pulses [Malkin and Fisch, Phys. Rev. E 101, 023211 (2020)], we perform the first numerical simulations in one dimension to illustrate amplification of a short high frequency seed through four-wave mixing. We illustrate how parasitic processes including phase modulation and spatial pulse slippage limit the amplification efficiency. Although the regimes studied were not where the optimal efficiencies were expected, these regimes do expose the basic physical processes at play, while still yielding not insignificant spectral power upshift.
Experimental demonstration of a three-dimensional acoustic hyperlens for super-resolution imaging
Authors: Hu Chengbo , Weng Jingkai , Ding Yujiang , Liang Bin , Yang Jing , Cheng Jianchun
Published: May 2021

Acoustic hyperlenses have recently attracted much attention for promising applications in various fields. Yet the experimental realization of an acoustic hyperlens working in a real three-dimensional (3D) world is still lacking. Here, we theoretically propose and experimentally demonstrate a 3D acoustic hyperlens capable of producing super-resolution imaging for broadband airborne sound. A simple nonresonant metamaterial is designed as a practical implementation that simultaneously ensures tessellation of the curved surface and deep-subwavelength resolution. We analyze the dispersion relationship of the designed metamaterial that converts the evanescent waves into radially propagating modes based on positive extreme anisotropy. The effectiveness of our mechanism is demonstrated both numerically and experimentally via the production of 3D magnifying super-resolution imaging of small objects containing subwavelength patterns within a broad frequency range. We envision the realization of a 3D acoustic hyperlens to offer possibilities for the design of acoustic super-resolution imaging devices and their application in diverse scenarios ranging from medical ultrasound imaging to noninvasive evaluation.
Quantum flexoelectric nanobending
Authors: Zypman Fredy
Published: May 2021

The aim of this article is twofold. First, to develop a clear quantum theoretical playground where questions about the connection between strain fields and electric fields could be unambiguously explored. Second, as an application, to derive a criterion that establishes the length scale below which bent molecules, in particular, carbon nanotubes, display flexoelectricty. To this end, we consider a model molecule that displays the basic elements necessary to support flexoelectricity. Due to its simplicity, a full quantum mechanical solution is possible, providing analytical expressions for the energy bands and for the electronic states and their corresponding strain gradient-induced charge density. This charge density is in turn used to evaluate the appearance of electric fields. Finally, we investigate the consequences of applying our model to real organic ring systems, in particular, answering the question of whether flexoelectricity found in the theory should be present in experiments.
Self-energized organic-inorganic hybrid composite for surface enhanced Raman spectroscopy
Authors: Alvarez-Ruiz Diana T. , Almohammed Sawsan , Fularz Agata , Barwich Sebastian Tade , Rice James H.
Published: May 2021

In this study, we integrate plasmonic metal nanomaterials with a piezoelectric polyvinylidene fluoride (PVDF) polymer and lithium niobate (LiNbO3) based composite to form an all-solid-state flexible self-energized sensor. We demonstrate that following the application of a load, the film enhances the surface-enhanced Raman spectroscopy (SERS) signal of an analyte molecule up to 14 times. The piezoelectric β-phase of PVDF in the film is optimized through the introduction of multi-walled carbon nanotubes and post-fabrication UV irradiation annealing. Additionally, the SERS signal enhancement can be further increased by the application of in situ UV light irradiation of the sample, resulting in the generation of photoexcited electrons from LiNbO3 microparticles introduced into the composite. Both the application of a mechanical displacement and the UV light-induced charge generation result in an improved charge transfer between the film and an analyte molecule. The piezoelectric PVDF/LiNbO3 film has been shown to be a suitable SERS platform for the detection of important biological molecules, demonstrating the potential of the substrate for fast on-site detection applications.
Flexoelectricity in metals
Authors: Yurkov A. S. , Yudin P. V.
Published: May 2021

Flexoelectricity is an electromechanical phenomenon that, unlike piezoelectricity, is present in any material. While the largest flexoelectric response is observed in ferroelectrics and related materials, its manifestations in various other materials are of great interest for a broad scope of scientific and industrial tasks. Here, we provide a simple theoretical model for flexoelectricity in metals. This is done in terms of continuum mechanics. Estimates for aluminum are provided, and guidelines for an experimental detection of the phenomenon are formulated. The magnitude for the flexoelectric effect in metals is found to be comparable with that in high-k dielectrics, which makes metals just as good as other materials for applications in flexoelectric sensing and energy harvesting. Besides, in metals, flexoelectricity may be easier to interpret because it is predicted to be free of surface contributions.
A hybrid percolation transition at a finite transition point in scale-free networks
Authors: Choi K. , Choi Wonjun , Kahng B.
Published: May 2021

Percolation transition (PT) means the formation of a macroscopic-scale large cluster, which exhibits a continuous transition. However, when the growth of large clusters is globally suppressed, the type of PT is changed to a discontinuous transition for random networks. A question arises as to whether the type of PT is also changed for scale-free (SF) network, because the existence of hubs incites the formation of a giant cluster. Here, we apply a global suppression rule to the static model for SF networks and investigate properties of the PT. We find that even for SF networks with the degree exponent 2<λ<3, a hybrid PT occurs at a finite transition point tc, which we can control by the suppression strength. The order parameter jumps at tc− and exhibits a critical behavior at tc+.
Data enriched lubrication force modeling for a mechanistic fiber simulation of short fiber-reinforced thermoplastics
Authors: Kugler Susanne K. , Bechara Abrahán , Perez Hector , Cruz Camilo , Kech Armin , Osswald Tim A.
Published: May 2021

The simulative prediction of fiber orientation for injection-molded short fiber-reinforced thermoplastics is an important step in prediction warpage and failure of injection molded parts. There exists a variety of phenomenological macroscopic fiber orientation models, which are computationally very efficient but strongly dependent on phenomenological parameters. This research focuses on a mechanistic fiber orientation model for concentrated short fiber-reinforced thermoplastics. A fully coupled computational fluid dynamics particle simulation is used to estimate the lubrication forces between two fibers in different configurations (angles between fibers, velocities) with varying fiber length and surrounding fluid viscosity. Based on these data, a calibrated lubrication model is developed and implemented in a mechanistic fiber orientation simulation. In addition, the fiber orientation estimated by the enhanced mechanistic fiber model is compared to experimental fiber orientation data obtained with a glass fiber-reinforced thermoplastic industrial grade, which showed an improvement over a simulation that did not include the lubrication force.
Low temperature carbon co-implantation in silicon: Defects suppression and diffusion modeling
Authors: Dumas P. , Julliard P.-L. , Borrel J. , Duguay S. , Hilario F. , Deprat F. , Lu V. , Zhao W. , Zou W , Arevalo E. , Blavette D.
Published: May 2021

Carbon has been co-implanted to phosphorus at low temperature (−100 °C) in silicon. As compared to a room temperature carbon implant, phosphorus activation is increased due to the suppression of extended defects. The unusual carbon depleted region observed in both secondary ion mass spectroscopy and atom probe tomography annealed profiles has been explained and modeled using an interstitialcy diffusion barrier of 0.6 eV. Carbon clusters have been interpreted as being composed of several immobile dimers carbon/self-interstitial, in agreement with the stoichiometry of the SiC phase. From the model presented here, an adequate temperature window (>750 °C) has been found regarding self-interstitials trapping by carbon.
Improvement of the ultra-low-frequency active vertical vibration isolator with geometric anti-spring structure for absolute gravimetry
Authors: Yao Jiamin , Wu Kang , Guo Meiying , Wang Lijun
Published: May 2021

For absolute gravimeters, which play important roles in geophysics and geological exploration, an ultra-low-frequency vertical vibration isolator is necessary to achieve the required measurement precision. A novel active vibration isolator that uses a geometric anti-spring (GAS) structure has been proposed by our team at Tsinghua University previously, but its performance is mainly limited by the large-scale drift in the detection signal of the system. In this paper, after a brief theoretical introduction to the overall system, recent improvements in this novel vibration isolator are presented. The main improvements to the isolator are the use of new blades in the GAS structure and the addition of an extra compensation circuit to eliminate the drift. The improved prototype has a resonance period of 29.2 s and a continuous working time of several days, as compared with the resonance period of 19.2 s and a working time lasting only several minutes of the previous prototype. Experiments show that the improved prototype performs well in the homemade T-1 laser-interferometry absolute gravimeter. The standard error of the mean (SEM) of a 50-drop measurement performed in Tsinghua University is reduced significantly from 404 μGal (1 μGal = 1 × 10−8 m s−2) without the vibration isolator to 10.8 μGal with the improved prototype at its best level. Additionally, the SEM of a 50-set measurement (including 800 drops) lasting for 25 h achieves 5.9 μGal with the improved prototype.
Unsteady shock interaction mechanisms of high enthalpy reacting flows over double wedges at Mach 7
Authors: Vatansever D. , Celik B.
Published: May 2021

A recently developed and validated open-source nonequilibrium Navier–Stokes solver, hyperReactingFoam is used for analyses of Mach 7 flows of air with 8.0 megajoules per kilogram (MJ/kg) stagnation enthalpy over double wedges with four distinct aft angles of 45°, 50°, 55°, and 60°. The validation studies contain both qualitative and quantitative comparisons of the obtained results with experimental and two numerical results available in the literature for the 30°–55° double wedge model. Physics and characteristics of the flows are revealed by comparing the shock structures, chemical compositions, surface pressure, and wall heat flux distributions of each aft angle. It is seen that increased aft angle significantly enhances the magnitudes of wall heat flux and surface pressure. Fluctuations of wall heat flux and surface pressure distributions in time significantly increase along the second wedge surface in the case of higher aft angles. Faster chemical reaction rates take place also for larger aft angles, regardless of the assumption of the flow to be in thermal equilibrium or nonequilibrium. The flow is observed to be chemically frozen downstream of the expansion corner. Time-averaged wall heat flux magnitudes of the flow for the aft angle values of 55° and 60° are found to be three times larger than of the flow with 2.1 MJ/kg stagnation enthalpy.
Permeability variation analysis using the superficial diameter correlation with porosity change
Authors: Shin Chang Hoon
Published: May 2021

Permeability characterization is a major factor for ensuring more environment-friendly operations and economically viable industrial applications related to carbon capture sequestration, hydrocarbon recovery, nuclear waste disposal, and remediation in groundwater. Regardless, the permeability variation caused by changes in formation stress is simply defined as the power-law function of porosity. An alternative formula can be presented using the Kozeny–Carman equation based on hydraulic diameter and tortuosity. However, the hydraulic tortuosity and the Kozeny constant cannot be precisely measured because of the extremely complex and microscale pores. Accordingly, this study considers the Kozeny–Carman equation for presenting the other definable variables and more general correlations for performing permeability variation analyses. Herein, the effective tortuosity and effective and superficial diameters of porous media are deduced adopting the conventional viscous flow theory. Subsequently, the Kozeny–Carman equation is improved by replacing the immeasurable variables with the effective variables. The correlations of all the key geometric variables with permeability variation are investigated via pore-scale simulations based on two types of 20-series porous medium models with a wide range of porosity (13.4%–47.4%) and permeability (0.0073 –18.3 Darcy). Herein, several impressive functional aspects of the superficial diameter were discovered with porosity changes, such as quadratic functional correlations, parallel shifts for each flow path, and less sensitive variations in low porosity ranges. Consequently, this study proved that permeability variations can be more precisely and generally estimated using the quadratic correlations of the superficial diameter with porosity changes.