bluuebunny/crossref_metadata_2025 huggingface dataset:
Toward high-performance p-type, tin-based perovskite thin film transistors
Authors: You Insang , Noh Yong-Young
Published: June 2021

Metal halide perovskites (MHPs) have been intensively investigated for use in solar cells and light-emitting diodes. However, the research into their applications in thin film transistors (TFTs) has drawn less attention, in spite of their high intrinsic charge mobility. In this Perspective, we provide a brief overview of the development of high-performance Sn-based perovskite TFTs. Initially, the advantages of Sn-based MHPs for TFTs are defined. Next, some recent studies on improving the device performance are introduced. Finally, challenges that need to be addressed to achieve high-performance TFTs are highlighted.
Non-equilibrium charge density wave ground state of quasi-two-dimensional rare-earth tritelluride TbTe3
Authors: Frolov A. V. , Orlov A. P. , Voropaev D. M. , Hadj-Azzem A. , Sinchenko A. A. , Monceau P.
Published: June 2021

We have studied the time dependence of the relaxation of the non-equilibrium charge density wave (CDW) toward an equilibrium ground state in TbTe3 when the sample is cooled through the Peierls transition temperature under an electric field down to a given temperature, Texp. We show that when cooled at zero electric field or a value less than the threshold one, Et, for depinning the CDW at Texp, the CDW equilibrium ground state has a single phase in the sample volume. When cooled with an electric field higher than Et, the CDW ground state is in a frozen glass state, which can be destabilized only by reducing the electric field below Et. We tentatively interpret these results by the interaction of the CDW with a well ordered Te–Te discommensuration network.
Self-formation of high-field domain in epitaxial ZnO and its suppression in ZnO/MgZnO heterostructure
Authors: Šermukšnis E. , Liberis J. , Šimukovič A. , Matulionis A. , Ding K. , Avrutin V. , Özgür Ü. , Morkoç H.
Published: June 2021

Microwave noise is used to study high-electric-field electronic properties of ZnO channels with electron densities in the range from 1017 to 1019 cm–3. The strong source of noise is observed to superimpose onto the standard hot-electron noise governed by the hot-electron energy relaxation. At a given current, the excess noise temperature ΔTn increases with the channel length, and values up to and above 10 000 K are reached. The steep dependence ΔTn∝I12 on the current I approximately holds for the longest channels. The source of noise in question is suppressed in ZnO epilayers at high electron densities and in a ZnO/MgZnO heterostructure with two-dimensional electron gas. The observed results are evaluated and discussed in terms of the self-formation of high field domains. The estimated domain voltage Ud increases with the current; the dependence is close to Ud∝I6. The domain self-formation is additionally confirmed by measuring the spectral density of current fluctuations; the usual hot-electron noise turns into shot noise as the current increases. The Fano factor demonstrates an increasing number of nearly ballistic electrons that traverse the self-supporting domain.
Spin dynamics in GaN/Al0.1Ga0.9N quantum well with complex band edge structure
Authors: Zhang Shixiong , Tang Ning , Liu Xingchen , Zhang Xiaoyue , Fu Lei , Zhang Yunfan , Fan Teng , Sun Zhenhao , Ge Weikun , Shen Bo
Published: June 2021

Spectrally distinguished spin relaxation dynamics in a single GaN/Al0.1Ga0.9N quantum well was investigated by a time-resolved Kerr rotation spectrum at room temperature. Three spin relaxation processes were well distinguished by a photon energy upon the excitation energy being resonated with the bandgap of various layers. It is observed that the electron spin relaxation time of 7 ps in a GaN quantum well is much shorter than that of 140 ps in an Al0.1Ga0.9N barrier layer due to the considerable polarization electric field at a GaN/Al0.1Ga0.9N heterointerface. For electrons in bulk GaN and Al0.1Ga0.9N, the dominant role of electron–photon scattering and alloy disorder scattering in the anisotropic D'yakonov–Perel’ (DP) relaxation was revealed by the photoexcited electron density and magnetic field dependence of the spin relaxation time.
Non-degenerate parametric mixing and Q-enhancement in ALN Lamb wave resonator
Authors: Lu Ting , Schneider Joseph D. , Tiwari Sidhant , Zou Xiating , Yeung Lap K. , Candler Robert N. , Carman Gregory P. , Wang Yuanxun Ethan
Published: June 2021

In this Letter, we explore a non-degenerate phase independent parametric quality factor (Q)-enhancement technique for aluminum nitride (AlN) Lamb wave resonators. Unlike other active Q-enhancement techniques which require precise phase control of the electronic feedback loop, this technique is implemented by parametrically pumping AlN material stiffness to realize a negative resistance seen at the signal path. The negative resistance is dependent on the nonlinear material modulation and multi-resonance coupling in the device. A nonlinear circuit model is developed to simulate the parametric coupling of each resonance and extract the nonlinearity of AlN from experimental data. With proper pump frequency and pump power, the device quality factor is boosted in both simulation and experiment. The demonstrated Q-enhancement method is simple to implement and can be applied to other types of resonators that have nonlinear behavior and support multi-resonance operation.
Interface-driven electrical magnetochiral anisotropy in Pt/PtMnGa bilayers
Authors: Meng K. K. , Chen J. K. , Miao J. , Xu X. G. , Jiang Y.
Published: June 2021

Nonreciprocal charge transport, which is frequently termed as electrical magnetochiral anisotropy (EMCA) in chiral conductors, touches the most important elements of modern condensed matter physics. Here, we have investigated the large EMCA in Pt/PtMnGa (PMG) bilayers, which can be attributed to the nonreciprocal response of an interface-driven chiral transport channel. Different from the traditional linear current-dependent EMCA, for Pt/PMG bilayers, higher-order EMCA coefficients should be phenomenally added especially for the small current region. This unusual behavior has been explained based on both quantum transport and semiclassical transport models. Furthermore, a combination of asymmetrical electron scattering and spin-dependent scattering furnish the PMG thickness-dependent chiral transport behaviors in Pt/PMG bilayers. The dramatically enhanced anomalous Hall angle of PMG further demonstrates the modified surface state properties by strong spin–orbit coupling.
Adsorbate-assisted migration of the metal atom in atomically dispersed catalysts: An ab initio molecular dynamics study
Authors: Humphrey Nicholas , Bac Selin , Mallikarjun Sharada Shaama
Published: June 2021

We present a phenomenological study of dynamical evolution of the active site in atomically dispersed catalysts in the presence of reaction intermediates associated with CO oxidation and low-temperature water–gas shift reaction. Using picosecond ab initio molecular dynamics, we probe the initiation of adsorbate-induced diffusion of atomically dispersed platinum on rutile TiO2(110). NVT trajectories spanning 5 ps at 500 K reveal that the dynamical stability of the metal atom is governed by its local coordination to the support and adsorbate. Adsorbates that bind the strongest to Pt typically also lead to the fastest diffusion of the metal atom, and all adsorbates weaken Pt-support interactions, resulting in higher diffusion coefficients compared to bare Pt. We note, however, the absence of quantitative correlations between adsorption characteristics (Pt Bader charge, adsorbate binding energy) and ensemble-averaged quantities (diffusion coefficients). A recurring structural motif identified in several trajectories is a near-linear coordination between support oxygen, Pt, and specific adsorbates. These geometries, on account of enhanced metal support interactions, stabilize Pt and inhibit migration over picosecond timescales. We also identify hydrogen bonding events between the adsorbate and support for OH-containing groups. In the case of OH-bound Pt, for instance, we believe that short-lived H-bonds between OH and support promote Pt migration in the beginning of the NVT trajectory, while the subsequent formation of a near-linear geometry stabilizes the Pt atom despite the continued formation of short-lived hydrogen bonds. These observations are consistent with prior studies that report stabilization of isolated metal atoms in the presence of hydroxyl groups.
Li-based selenized Cu2ZnSnS4 surface: Possible route to overcoming voc-deficit of kesterite solar cells
Authors: Zhao Ke , Xiang Huiwen , Cui Yingru , Zhu Rui , Liu Chengyan , Jia Yu
Published: June 2021

Usually, open-circuit voltage (Voc) of thin film solar cells significantly depends on the band bending at the front interface of an absorber/buffer. The failed band bending at a Cu2ZnSnS4/CdS (CZTS/CdS) interface severely hinders the increase in Voc due to the excessively high concentration of holes at the CZTS side. Alleviating the strong p-type or converting it to weak n-type at the CZTS surface is a credible idea to overcome the Voc− deficit. First-principles calculations show that the Li-based selenized CZTS surface presents the desired property with excellent advantages: (i) The greatly improved defects and band offset suppress carrier nonradiative recombination and facilitate electrons transmission, respectively. (ii) Its intrinsic weak n-type characteristic effectively promotes the large band bending at the interface.
Broad magnetic anisotropy regulation in as-deposited Pt/Co/MgO multilayers by tuning electronic coordination
Authors: Zhao Yongkang , Li Yukun , Meng Fei , Xie Shuai , Xu Xiulan , Li Baohe , Feng Chun , Yu Guanghua
Published: June 2021

The regulation in the magnetic anisotropy of magnetic films is crucial for developing the magnetic storage and logic devices. The traditional work achieved an effective tunability of the magnetic anisotropy by a subsequent processing of the as-deposited film, such as a post-annealing treatment or electric field application. Here, we proposed an effective method to achieve a direct and broad tunability of the magnetic anisotropy in the as-prepared film by adjusting electronic coordination. Nitrogen (N) atoms were doped in the Co layer of Pt/Co/MgO multilayers to effectively control the electronic coordination of Co and enhance the 3dz2–r2 orbital occupancy of Co for modulating the Co–O orbital hybridization. Consequently, the magnetic anisotropy of the as-deposited film changed from in-plane to perpendicular direction with the N doping, resulting in a significant increment in the magnetic anisotropy energy by 2.48 × 106 erg/cm3. Furthermore, the critical Co thickness with maintaining the perpendicular magnetic anisotropy was enlarged from 1 to 3 nm, which is beneficial for enhancing the stability of nanodevices. These findings provide an effective strategy to tune the magnetic anisotropy of magnetic films toward the applications of various magnetic storage and logic devices.
Betweenness centrality of teams in social networks
Authors: Lee Jongshin , Lee Yongsun , Oh Soo Min , Kahng B.
Published: June 2021

Betweenness centrality (BC) was proposed as an indicator of the extent of an individual’s influence in a social network. It is measured by counting how many times a vertex (i.e., an individual) appears on all the shortest paths between pairs of vertices. A question naturally arises as to how the influence of a team or group in a social network can be measured. Here, we propose a method of measuring this influence on a bipartite graph comprising vertices (individuals) and hyperedges (teams). When the hyperedge size varies, the number of shortest paths between two vertices in a hypergraph can be larger than that in a binary graph. Thus, the power-law behavior of the team BC distribution breaks down in scale-free hypergraphs. However, when the weight of each hyperedge, for example, the performance per team member, is counted, the team BC distribution is found to exhibit power-law behavior. We find that a team with a widely connected member is highly influential.
Understanding the needs and use of sexual and reproductive health services among Thai women: a descriptive cross-sectional study in Sweden
Authors: Åkerman Eva , Larsson Elin C. , Essén Birgitta , Westerling Ragnar
Published: June 2021

Background Immigrants are at increased risk of HIV infection in Europe and at risk of delayed diagnosis. In Sweden, Thailand belongs to one of the three most common countries of origin among immigrants diagnosed with HIV. This study investigated the need and use of sexual and reproductive health (SRH) services among Thai women residing in Sweden. Use of contraceptives and HIV testing in Thailand was also investigated to understand if this influences utilisation of SRH services in Sweden. Methods: A cross-sectional study using postal questionnaire to all Thai-born women (age 23–60) in Stockholm, residing in Sweden since 2014. The response rate was 52.3% (n= 266). Bivariate and multivariate logistic regression analyses were used. Results: The majority reported a significant need for information related to SRH services. Most of the women using contraception (70%) bought their contraceptives in Thailand. In total, 60% of the women had been HIV-tested at some point in their lives; the majority were tested in Thailand. Women who had been HIV-tested in Thailand were more likely to also have been tested in Sweden. Significant differences in contraception use, participation in contraceptive counselling and having had an HIV test were found between groups of younger and older women. Conclusions: Our findings imply that age is an important factor to understand women’s need and use of SRH services in Sweden versus Thailand. Furthermore, women’s lack of knowledge and reported need for SRH information needs to be considered when making policies and strategies to increase access to SRH services.
Hepatitis C virus infection in HIV-infected men in Singapore, 2006–2018: incidence and associated factors
Authors: Ang Li Wei , Choy Chiaw Yee , Ng Oon Tek , Leo Yee Sin , Wong Chen Seong
Published: June 2021

Background The epidemiology of hepatitis C virus (HCV) infection in people living with HIV has been evolving, with increasing evidence of permucosal (sexual) transmission identified predominantly in HIV-positive men who have sex with men (MSM). The aim of this study was to estimate the incidence rate and elucidate epidemiological factors associated with HCV infection among HIV-infected men in Singapore from 2006 to 2018. Methods: A retrospective cohort study was conducted using a clinical database maintained by the Clinical HIV Program at the National Centre for Infectious Diseases, Singapore. Factors associated with incident HCV infections were identified using Cox proportional hazards regression analyses. Results: Among 1348 HIV-infected male patients who were HCV seronegative at baseline, 64 (4.7%) subsequently tested positive for HCV, giving an incidence of 0.88 per 100 person-years of follow-up (PYFU) (95% confidence interval (CI) 0.69–1.13). The incidence rate of HCV seroconversion increased from 0.33 (95% CI 0.12–0.71) per 100 PYFU in 2010–2012 to 1.93 (95% CI 1.36–2.67) in 2016–2018. Independent factors associated with incident HCV infection were younger age groups at HIV diagnosis versus ≥45 years, HIV acquisition via MSM or via both sexual contact and intravenous drug use versus heterosexual transmission, HIV diagnosis in later periods versus 2006–2009, and recent syphilis acquisition. Conclusions: An increasing trend of incident HCV infection was seen in HIV-infected men, particularly for MSM. Preventive and behavioural interventions should be targeted at HIV-infected individuals engaged in high-risk sexual behaviour.
Forms of inorganic phosphorus in carbonatic soils in the Pantanal of Mato Grosso do Sul, Brazil
Authors: de Souza Oliveira Naelmo , Schiavo Jolimar Antonio , Laranjeira Laís Thomaz , de Moraes Eloise Mello Viana , Lima Miriam Ferreira , Nunes Geisielly Pereira , Pereira Marcos Gervasio
Published: June 2021

The western region of the southern Pantanal is characterised by soils with high phosphorus (P) contents, derived from materials from the surrounding lithostratigraphic units, accumulated by fluvial transport. However, studies on forms and availability of P in these soils are scarce. The objective of this study was to evaluate the different forms of inorganic P and their relationship with some attributes of carbonatic soils in the Pantanal of Mato Grosso do Sul, Brazil. Hedley’s sequential fractionation scheme was used to evaluate the forms of P in soil profiles: Kastanozems (profiles P1 and P3) and Gleysol (profile P2). Total P contents were similar in the three profiles, 3782–5637 mg kg–1, with mean values of 22% for organic P and 46% for inorganic P (P.i). The P.i results indicated that in the profiles there was a predominance of inorganic forms of P in the following order: P-NaOH 0.5 mol L–1 > P-NaHCO3 > P-NaOH 0.1 mol L–1 > P-HCl, that is, adsorbed to microaggregates, labile, adsorbed to oxides and precipitated with calcium (Ca), respectively. The highest values of total organic P were verified in the surface horizons, with high correlation with total P contents. Residual P contents were high in all profiles, representing 29.0–33.3% of the total P, being correlated with CaCO3 contents. The studied profiles had high contents of labile P, with the highest values in the fraction P.i-NaHCO3, possibly associated with the processes of reduction of iron during the periods of floods, making the adsorbed P available. The contents of P.i-NaOH 0.1 mol L–1, a moderately labile fraction adsorbed to oxides, showed few differences compared to the non-labile fractions associated with Ca (P.i-HCl). Possibly, organic matter was bound to Ca, inhibiting the formation of precipitates of Ca with P and making P available for the more labile fractions.
CALM supports clathrin-coated vesicle completion upon membrane tension increase
Authors: Willy Nathan M. , Colombo Federico , Huber Scott , Smith Anna C. , Norton Erienne G. , Kural Comert , Cocucci Emanuele
Published: June 2021

Significance

Clathrin-coated vesicles (CCVs) are endocytic carriers responsible for the internalization of receptor-bound ligands and extracellular fluids. CCV assembly occurs by the sequential recruitment of clathrin, adaptors, and other accessory molecules that promote curvature formation. To form, CCVs need to overcome the local plasma membrane tension that varies during cell cycle, development, and cell polarization. Using quantitative fluorescence microscopy, we demonstrate that the adaptor CALM is a major determinant of CCV formation upon membrane tension increase. Since CALM is differentially expressed, our results demonstrate that competence in clathrin-mediated endocytosis is tissue specific, providing mechanistic explanation why CALM depletion strongly affects embryo development and red blood cell differentiation with minor effects in other systems.
Climate and land-use changes interact to drive long-term reorganization of riverine fish communities globally
Authors: Comte Lise , Olden Julian D. , Tedesco Pablo A. , Ruhi Albert , Giam Xingli
Published: June 2021

Significance

Understanding the mechanisms by which biological communities are reorganized by environmental change is a key question facing ecologists. Using a global database of fish abundance time series spanning recent decades, together with community-level indices describing species temperature and flow affinities, we show that two important aspects of climate change (water temperature and streamflow alteration) are interacting with land-use modification to drive increases in the dominance of species that prefer warm- and slow-water habitats. Although these community reorganizations show substantial geographical variation, they can be explained by a combination of degree of environmental changes and initial community composition. These findings offer insights to improve ecological forecasting in the future to better inform and prioritize conservation actions in freshwater ecosystems.
Photosynthesis-independent production of reactive oxygen species in the rice bundle sheath during high light is mediated by NADPH oxidase
Authors: Xiong Haiyan , Hua Lei , Reyna-Llorens Ivan , Shi Yi , Chen Kun-Ming , Smirnoff Nicholas , Kromdijk Johannes , Hibberd Julian M.
Published: June 2021

Significance

The ability of plants to initiate systemic responses to local biotic and abiotic stress is well known. One such example takes place after exposure to high-light episodes and involves an initial, local accumulation of reactive oxygen species (ROS) in the region exposed to excessive light. Overexcitation of the photosynthetic apparatus has long been known to lead to ROS production, but whether this is necessary and sufficient is not known. Here, we show that local synthesis of ROS also requires NADPH oxidases located in bundle-sheath strands and is not dependent on photosynthesis. As NADPH oxidases also allow the systemic ROS response, this work identifies a component that unifies both the local and systemic responses of plants to high light.
Stewardship of global collective behavior
Authors: Bak-Coleman Joseph B. , Alfano Mark , Barfuss Wolfram , Bergstrom Carl T. , Centeno Miguel A. , Couzin Iain D. , Donges Jonathan F. , Galesic Mirta , Gersick Andrew S. , Jacquet Jennifer , Kao Albert B. , Moran Rachel E. , Romanczuk Pawel , Rubenstein Daniel I. , Tombak Kaia J. , Van Bavel Jay J. , Weber Elke U.
Published: June 2021

Collective behavior provides a framework for understanding how the actions and properties of groups emerge from the way individuals generate and share information. In humans, information flows were initially shaped by natural selection yet are increasingly structured by emerging communication technologies. Our larger, more complex social networks now transfer high-fidelity information over vast distances at low cost. The digital age and the rise of social media have accelerated changes to our social systems, with poorly understood functional consequences. This gap in our knowledge represents a principal challenge to scientific progress, democracy, and actions to address global crises. We argue that the study of collective behavior must rise to a “crisis discipline” just as medicine, conservation, and climate science have, with a focus on providing actionable insight to policymakers and regulators for the stewardship of social systems.
Warm nights disrupt transcriptome rhythms in field-grown rice panicles
Authors: Desai Jigar S. , Lawas Lovely Mae F. , Valente Ashlee M. , Leman Adam R. , Grinevich Dmitry O. , Jagadish S. V. Krishna , Doherty Colleen J.
Published: June 2021

Significance

The effects of warmer nighttime temperatures (WNT) on crops are one poorly understood dimension of climate change. WNT result from the asymmetrical increase in nighttime versus daytime temperatures. In rice, WNT reduce grain yield and quality. WNT reduce the amplitude of daily temperature cycles plants use to set their circadian clock. Therefore, we examined how WNT affect the timing of molecular activities. In field-grown plants, WNT alter the daily pattern of the transcriptome. Genes with strong rhythmic expression and those under circadian control are affected most by WNT. Many candidate regulators of the disrupted genes are circadian clock associated, emphasizing the altered timing under WNT. The pathways and mechanisms identified can assist efforts to identify lines tolerant to WNT.
Hormone-dependent activation and repression of microRNAs by the ecdysone receptor in the dengue vector mosquito
Aedes aegypti
Authors: He Ya-Zhou , Aksoy Emre , Ding Yike , Raikhel Alexander S.
Published: June 2021

Significance

Mosquitoes transmit numerous devastating human diseases. MicroRNAs play important roles in mosquito reproduction, but how their expression is controlled remains poorly understood. We demonstrate that ecdysone receptor (EcR) dynamically regulates the expression of clustered
miR-275
and
miR-305
to coordinate their activity with the demands of the female
Aedes aegypti
reproduction. EcR represses their expression at the low 20-hydroxyecdysone (20E) level before blood feeding by interacting with the corepressor SMRTER, the insect analog of the vertebrate nuclear receptor corepressors SMRT and N-CoR. In contrast, it activates their expression at the high 20E level after a blood meal via replacement of SMRTER with the coactivator Taiman. Our study gives valuable clues for miRNA utilization to control mosquito populations and, thus, mosquito-borne diseases.
Regulation of Dishevelled DEP domain swapping by conserved phosphorylation sites
Authors: Beitia Gonzalo J. , Rutherford Trevor J. , Freund Stefan M. V. , Pelham Hugh R. , Bienz Mariann , Gammons Melissa V.
Published: June 2021

Significance

We report a Dishevelled structural clamp, a β-sheet containing a conserved phosphorylation site immediately upstream of the Dishevelled, Egl-10, and Pleckstrin (DEP) domain, contacting a cognate surface on its partner DEP domain to stabilize the domain-swapped dimer. DEP dimers are essential for Wnt/β-catenin signal transduction, but because the Frizzled receptor–binding surface of the DEP monomer is masked in the dimer, domain swapping may need to be attenuated to sustain prolonged Frizzled binding that is needed to transduce noncanonical Wnt signals. Mutation of this phosphorylation site and, by implication, its phosphorylation destabilize DEP dimers, thereby disabling canonical signaling. We propose that the regulation of DEP domain swapping by phosphorylation provides a mechanism whereby Dishevelled could switch off canonical Wnt signals.
Cermet materials reinforced with a small addition of spinel nanoparticles for molten salt power systems
Authors: Agureev L E , Ivanov B S , Laptev I N , Ivanov A V , Ashmarin A A
Published: June 2021

This work is devoted to developing of new cermets for molten-salt power systems, promising for use in aviation, rocket and space technology, and power engineering. The production of cermets in the nickel-aluminum alloy system - 35 wt. % aluminum oxide by the method of mechanical activation and spark plasma sintering was carried out. It was found that the addition of 5 wt. % yttrium oxide, as well as small quantities (0.1 wt. %) of aluminum-magnesium spinel nanoparticles, increase the strength of the cermet at elevated temperatures. Cermets have high strength at room and elevated temperatures, which amounted to 480-530 MPa at 20 °C and 430-470 MPa at 750 °C. The micro structure of cermets was characterized by the presence of elliptical regions, the grains in which were significantly smaller than the grains in the surrounding matrix. This structure allows to effectively harden the material because elliptical areas are obstacles to crack propagation. Elliptical zones have length ranged 100 to 200 μm and width 5 to 20 μm. It was found that the material of the NiAl-Al2O3 system at 20 °C and 800 °C contains the phases NiAl, Al2O3, and Ni2Al3. Composite composition NiAl-Al2O3-Y2O3 at 20 °C and 800 °C retains the three-phase composition of NiAl, Al2O3, and Y2O3. Both materials are stable up to 800 °C.
Numerical study of the main rotor steep descent modes in the vortex ring state area
Authors: Makeev P , Ignatkin Yu , Shomov A
Published: June 2021

The research has been focused on aerodynamic characteristics of the Mi-8 helicopter main rotor in the hover and steep descent modes at rotor angles of attack αR = 90-30º, including vortex ring state area. The research is based on the original free wake model developed by the authors at Moscow Aviation Institute. Total and distributed aerodynamic characteristics, rotor wake shapes and streamlines have been calculated and analyzed. The vortex ring state area borders in the Vx-Vy
(horizontal and vertical flight speed components) coordinates have been defined. Five criteria are used: growth of the required rotor blade pitch angle; growth of rotor power consumption with a fixed rotor thrust; increase of the averaged value of the induced velocities and amplitudes of the rotor thrust and torque pulsations. The calculation results have been compared with experimental and calculation data of other authors and indicate sufficient reliability and applicability of used free wake model for calculation and analysis of the vortex ring state modes of helicopter rotor. The results presented in the paper can also significantly supplement the available results of experimental and computational studies of the helicopter rotor operation at steep descent modes in the vortex ring state area.
Fast prediction method of aircraft noise with distributed propulsion in the far field
Authors: Chen B , Yakovlev A A , Moshkov P A
Published: June 2021

Based on the known methods for calculating the propeller noise, a fast prediction method of the distributed propulsion noise is proposed. The method takes into account only the component of tonal noise from the load. To test the adequacy of the model, the GL-10 model was used, a concept of an aircraft developed by National Aeronautics and Space Administration to test distributed propulsion as well as vertical take-off and landing maneuvers. The comparison showed a good agreement between the results obtained and the data for the GL-10 model.
Local coordinates in problem of the orbital stability of pendulum-like oscillations of a heavy rigid body in the Bobylev–Steklov case
Authors: Bardin B S
Published: June 2021

In this paper a method is proposed for constructing a nonlinear canonical change of variables, which makes it possible to avoid the singularity when introducing local coordinates in the neighborhood of periodic orbit of the autonomous Hamiltonian system with two degrees of freedom. As an application of this method, orbital stability of pendulum-like oscillations of a heavy rigid body with a fixed point in the Bobylev-Steklov case is investigated. In particular, it is performed a nonlinear study of the orbital stability for the so-called case of degeneracy, when it is necessary to take into account terms of order six in the Hamiltonian expansion in a neighborhood of the unperturbed periodic orbit.
Research of synthetic corundum in plunger pairs of power hydraulics
Authors: Puzanov A V , Kosorukova O V , Kotov V V
Published: June 2021

The development of hydraulic technologies requires the use of new structural materials. The study used the main provisions of the theory of positive displacement hydraulic machines and hydraulic drives and methods for their solution using multiphysics software. The article presents the results of a comparative analysis of the performance of plunger pairs made of synthetic corundum in hydraulic machines of power drives. The effect of using synthetic corundum in hydraulic power drives is determined. Analysis of the obtained results makes it possible to conclude that when using synthetic sapphire as a plunger material, taking into account the preservation of structural geometry, maximum stresses are reduced by 4.7%, contact stresses by 4.7%, and deformation by 44%, with a decrease in weight by 49%.
Experimental study of nonlinearity of the mechanical properties of layered woven CFRP
Authors: Pavlova S A , Kishov E A , Pavlov A A , Selivanov S E
Published: June 2021

The article presents the results of an experimental study of the nonlinearity of the mechanical properties of layered composite materials made by vacuum infusion based on carbon fabrics and an epoxy resin. The analysis of existing approaches to the modeling of composite materials considering their physical nonlinearity is carried out. A method is proposed for taking into account the degradation of the properties of a composite material, based on the fact that the damage parameters are replaced by the functional dependence of elastic constants on deformations, based on experimental data. The results of the application of this method are given for the test data analysis of two types of layered woven carbon-fiber-reinforced-plastics with a cross-hatching structure.
Forecasting new product demand using machine learning
Authors: Smirnov P S , Sudakov V A
Published: June 2021

The problem of predicting demand for a new product based on its characteristics and description is critical for various industrial enterprises, wholesale and retail trade and, especially, for modern highly competitive sector of air transportation, since solving this problem will optimize production, management and logistics in order to maximize profits and minimize costs. Classic demand forecasting methods assume the availability of sales data for a certain historical period, which is obviously not the case when concerning a new product. Most research papers are limited either to a specific category of goods or use sophisticated marketing methods. This paper proposes the use of machine learning methods. We used data about new product demand from the Ozon online store. The input data of the algorithm are characteristics such as the price, name, category and text description of the product. To solve the regression problem, various implementations of the gradient boosting algorithm were used, such as XGBoost, Light GBM, Cat Boost. The forecast accuracy is now about 4.00. The proposed system can be used both independently and as part of another more complex system.
Smooth approximation of probability and quantile functions: vector generalization and its applications
Authors: Torishnyi R , Sobol V
Published: June 2021

In this paper, we provide an approximation method for probability function and its derivatives, which allows using the first order numerical algorithms in stochastic optimization problems with objectives of that type. The approximation is based on the replacement of the indicator function with a smooth differentiable approximation – the sigmoid function. We prove the convergence of the approximation to the original function and the convergence of their derivatives to the derivatives of the original ones. This approximation method is highly universal and can be applied in other problems besides stochastic optimization – the approximation of the kernel of the probability measure, considered in the present article as an example, and the confidence absorbing set approximations.
Control and analysis of quadcopter flight when setting a complex trajectory of motion
Authors: Bogatov N , Kostin A , Maiorov N
Published: June 2021

The article presents the solution to the problem of autonomous piloting of a quadcopter for a complex flight task to determine the positioning error. Mathematical model is proposed for the equation of the dynamics of angular motion in a connected coordinate system to solve this problem. The stages of elaboration and creation of a flight task are considered, a model based on directed graphs is presented, reflecting various options for organizing the movement of a quadcopter. Clover quadcopters were taken as the object of research. The study was carried out in the airfield of the laboratory of unmanned aerial systems of the Saint Petersburg State University of Aerospace Instrumentation (SUAI). Fragments of the program code for the implementation of autonomous piloting in Python are given. The flight mission consisted in the formation of the letters SUAI in space. The article discusses the necessary hardware, instrumental systems and camera modes of operation for fixing the movement of the quadcopter. As a result of the research, special photographs of the movement of the quadcopter are taken and the permissible range of positioning errors is determined for performing the flight task.
Landing system of a swarm of small unmanned aerial vehicles
Authors: Nazarov A , Vospitanyuk A , Pasechnikov R , Pasechnikov I
Published: June 2021

The distributed information-measurement and management landing system is proposed to ensure safe landing of a swarm of small unmanned aerial vehicles on a robotic platform. The requirements for the proposed landing system are developed and the system structure diagram is presented. It includes a distributed air traffic control and management system in the landing zone, a space-time unmanned aircraft holding area with an ordered toroidal structure, and a buffer landing zone. When a small unmanned aerial vehicle leaves a holding area for a landing line, it is recommended to use multiple access protocols. The paper specifies the combination of the main elements of the landing system structure diagram, the pattern and features of their functioning, and develops a generalized algorithm for managing a swarm of small unmanned aerial vehicles in the information-measurement and management landing system.
Emergency probability for aircraft vehicle
Authors: Nekhrest-Bobkova A , Burdina A
Published: June 2021

The probability of an emergency assessment is one of the most important problems in the aviation sector. Timely identification of possible equipment failure can be a solution of this problem, that saves people’s lives. The article considers existing methods for risk assessment. The comparison of these methods is carried out. As a result of this paper, the artificial neural network was designed. The set of vital input parameters was determined during the neural network development. All the input variables are divided into groups. The most promising and accurate approach for probability of an emergency assessing the was determined, which forms the basis of the mechanism for engineering accidents.
Concept for composition of hybrid flying multi-rotor platforms with distributed load and its experimental justification
Authors: Chemodanov V , Gavrilin K , Klimov I , Kotelnikova A
Published: June 2021

This paper discusses the main approaches to the development and construction of hybrid flying multi-rotor platforms with separation of lift control functions and angular stabilization functions, called by the authors “distributed load”. A significant factor that limits flight time for majority of multi-rotor platforms is the energy density limit of lithium polymer batteries, which are most commonly used. To solve this problem we analyzed possible ways to increase flight time: replacing the main type of energy carrier for a more energy-intensive one and use of hybrid systems with combination of popular lithium-polymer batteries and a more energy-intensive energy carrier. The analysis was supported by experimental data.
Preventive approach to ensuring the operational reliability of aircraft components
Authors: Papic L , Iosifov P A , Kirillin A V
Published: June 2021

The operational safety of technical systems, especially for civil airliners, is largely dependent on the organization of their maintenance. In this case, there are two possible main approaches: service according to the standard, when the information necessary for planning the frequency of service is determined based on the analysis of series of identical products; service according to the actual state, when the state of each specific product is monitored and limit values of parameters set for the product are not exceeded, determining the quality of its functioning, including its reliability and safety. The latter approach is preventive because possible parametric failures are prevented. Using a hypothetical example, the report demonstrates the benefits of transition to condition service, provides limitations and recommendations for using this approach in the maintenance plan creation process.
Methods for designing electrical equipment for testing VLSI used in aviation digital information systems
Authors: Smirnov K , Nazarov A , Ulyahin A
Published: June 2021

Very-large-scale integrated circuits are widely and successfully used in the artificial intelligence systems and digital signal processing systems on board modern aircraft and space apparatuses through the implementation of complete digital systems on a chip. However, the level of integration of very-large-scale integrated circuits according to Moore’s Law continues to double every 2 years, and today the test equipment for their functional control is working to the limit of its capabilities. Since the development of interface boards (the main unit of test electrical equipment) for testing microcircuits is currently carried out manually, the timing of the release of microcircuits is unacceptably increasing. This article presents the original methods for automating the design of an interface board circuit using the information contained in the test vectors. By eliminating the human factor from the development process of this board, time is significantly reduced and design errors are eliminated.
Development of a model for analyzing the impact of configuration integrity loss on the aircraft product cycle time duration
Authors: Konstantinov I , Tereshonkov V
Published: June 2021

One of the most important criteria in the production of modern aircraft is the length of the production cycle (lead-time). This indicator largely determines the commercial product success. In the framework of this work, issues of ensuring electronic layout and configuration integrity at various life cycle stages of a modern aircraft. The problem started in one aircraft enterprise in case of impossibility to provide assembly ability of different parts. A serious problem is the designation of tolerances on the parts dimensions. A model for eliminating contradictions in deviations created. One of the most important research questions is the issue of reducing the duration of the production cycle through optimization and control of the electronic layout and product configuration. Using modern approaches for setting product dimensional chains, using electronic layout optimization - a list of recommendations for the product design process developed. A methodology compiled to save the integrity of the digital layout at the various aircraft design stages. Was created simulating model which describe all assembly stages. The influence of configuration integrity loss on the product cycle time was shown.
Delphi study on the term ‘students’ conceptions’
Authors: Plotz T , Krumphals I , Haagen-Schützenhöfer C
Published: June 2021

The concept of students’ conceptions is central in science education and research. However, a concise and accurate definition of the German term ‘Schülervorstellungen’ (engl. students’ conceptions) is still absent. Therefore, a Delphi study, inviting more than 200 professors and postdoctoral researchers in the field of German-speaking physics education research (PER), was conducted. Main purpose was to find opinions about the necessity for a general definition and if possible, definitions used implicitly in the scientific community of PER. First results indicate a need for a concise definition, especially for its use in physics teacher education. Based on our results, a broader discussion among other subject educational research communities dealing with this term is necessary.
Analysis to Develop Computerized Adaptive Testing with the Force Concept Inventory
Authors: Yasuda J , Mae N , Hull M M , Taniguchi M
Published: June 2021

As a method to shorten the test time of the Force Concept Inventory (FCI), Computerized Adaptive Testing (CAT) is suggested. CAT is a test administered on a computer, where items (i.e. questions) are selected based on the responses of examinees to prior items. As a step of the development, we conducted analyses to find an optimal way for the administration of CAT with the FCI. Specifically, since CAT is based on Item Response Theory (IRT), we examined which IRT model is the most preferable. Using 2812 responses of the FCI of Japanese students, we estimated the item parameters of the One-, Two-, Three-, and Four-parameter logistic model of IRT and then we evaluated the statistics for the goodness of fit and for model selection. Based on the analysis, we suggest that the Two-parameter logistic model is the most preferable for the administration of CAT with the FCI.
Bringing the apple to the Moon
Authors: Pereira J A M
Published: June 2021

Newtonian gravity can be regarded as a hypothetic-deductive system where the inverse square law is the starting point from which gravitational phenomena are deduced. This operational form of presenting gravity endorses problem solving and seems to be predominant in the teaching practice. In contrast, regarding phenomena as a source for the development of the theory is also possible, of course, and can be advantageous to scientific education since it deals with model conception and construction. This article intends to introduce undergraduates to Newtonian gravity using its empirical basis, i.e. the free fall and the planetary motion, to deduce the universal law of gravitation. It also steps into the modern interpretation of gravitational phenomena i.e. Einstein’s general relativity, including a discussion on the instantaneous action at a distance in this context. This didactic presentation of the Newtonian theory of gravity is designed to reach a threefold equality, similar to those applied in the method of separation of variables in partial differential equations, where G is treated as a separation constant. By doing so, the universality of the gravitation constant emerges as a conclusion rather than a statement. A few historical remarks on the development of this topic are also highlighted.
FCHgo: Fuel Cells Hydrogen educational model for schools, an imaginative approach to hydrogen and fuel cell technology for young students and their teachers
Authors: Dumont E , Fuchs H U , Corni F , Contini A , Altiero T , Romagnoli M , Karwasz G P
Published: June 2021

In this paper we will describe didactic elements in the Horizon 2020 project FCHgo. This project is directed at children and adolescents between 8 and 18 years old. Its ultimate goal is to raise awareness for renewable energy sources, in particular hydrogen as a fuel and fuel cells for electric power. As part of the project, we are developing a toolkit for teachers and pupils, based upon a narrative approach to physical science and engineering. We believe the narrative approach to be best suited for this project because it allows us to take into account the cognitive tools available to pupils at various stages of their development.
Analysis of the explanations of pre-service physics teachers about the Faraday Cage Effect and the Pointed Conductor Effect
Authors: Garrido N , López V , Pintó R
Published: June 2021

We study the evolution of the explanations made by a group of pre-service physics teachers when experiencing with two different electrostatic phenomena: the Faraday Cage Effect and the Pointed Conductor Effect. By using a teaching and learning sequence (TLS) to help students improve their understanding about these two electrostatic effects, we find that these explanations improve when teachers are able to combine correctly the electric-field model with the charge-distribution model.
Laboratory of Thinking – diagnosis of teaching science subjects in Poland – physics perspective
Authors: GRECZYŁO T , SOKOŁOWSKA D , DERYŁO Ł
Published: June 2021

The paper presents and discusses selected results of national diagnosis of teaching science subjects – physics, biology, chemistry and geography in Poland. The research was carried out at the beginning of the 2017/2018 school year and was the next instalment of research initiated in 2011 by Educational Research Institute (IBE) in Warsaw [1]. Authors elaborate data as a collection of comprehensive results enabling the improvement of science teaching and learning, supporting the creation of legal regulations in the area of education, improving the formula of external examinations as well as teacher education. The discussed data are presented with a special focus on results connected to physics education.