bluuebunny/crossref_metadata_2025 huggingface dataset:
Robust method for broadband efficiency enhancement of electron photocathodes using optical interferences
Authors: Alexander A. , Gaowei M. , Mistry S. , Walsh J. , Liu F. , Evans-Lutterodt K. , Stavitski E. , Pavlenko V. , Smedley J. , Moody N.
Published: June 2021

We demonstrate the key features of an interference cathode using both simulations and experiments. We deposit Cs3Sb photocathodes on Ag to produce an interference enhanced photocathode with 2–5× quantum efficiency (QE) enhancement using a robust procedure that requires only a smooth metal substrate and QE monitoring during growth. We grow both an interference cathode (Ag substrate) and a typical photocathode (Si reference substrate) simultaneously to confirm that the effects are due to optical interactions with the substrate rather than photocathode composition or surface electron affinity differences. Growing the cathodes until the QE converges shows both the characteristic interference peaks during growth and the identical limiting case where the cathode is “infinitely thick,” in agreement with simulations. We also grow a cathode until the QE on Ag peaks and then stop the growth, demonstrating broadband QE enhancement.
Superconducting proximity effect in a van der Waals 2H-TaS2/NbSe2 heterostructure
Authors: Han Hui , Ling Jie , Liu Wenhui , Li Hui , Zhang Changjin , Wang Jiannong
Published: June 2021

Superconducting proximity effect in the heterostructures opens up access to engineer superconductivity at the interface, and has inspired substantial research interest in the past decade. Here, we fabricate the van der Waals 2H-TaS2/NbSe2 heterostructure through the mechanical exfoliation and dry transfer technique. Enhanced superconductivity in 2H-TaS2 flakes with increased superconducting transition temperature by about 0.8 K is observed. Such enhancement is believed to be related to the leakage of the Cooper pairs from NbSe2 flakes to 2H-TaS2 flakes. In addition, the critical current of the superconducting transition of NbSe2 flakes is also increased in the heterostructures, which is related to the strengthened pairing strength of Cooper pairs in NbSe2 flakes arising from the interfacial coupling between NbSe2 flakes and 2H-TaS2 flakes. Our findings will open perspectives for insight into the superconducting proximity effect in the van der Waals heterostructures.
Thermal conductivity of short tungsten disulfide nanotubes: A molecular dynamics study
Authors: Wan Jing , Tan Cong , Rong Yan , Zhang Lan , Cai Hai-Fang
Published: June 2021

The effects of length, diameter, temperature, and axial strain on the thermal conductivity of armchair and zigzag WS2 nanotubes are systematically investigated by nonequilibrium molecular dynamics simulations. It is found that the thermal conductivity gradually increases with the increase in the length, while it is insensitive to nanotube diameter variation. The thermal conductivity of armchair and zigzag WS2 nanotubes is remarkably reduced as temperature increases due to the increment of phonon–phonon scattering and reduction of the phonon mean free path. In addition, compressive strain can increase thermal conductivity due to increased contributions from low-frequency phonons, while the opposite is true in the case of tensile strain. The chirality has a slight influence on the thermal transport properties of the WS2 nanotube.
Giant exciton-enhanced shift currents and direct current conduction with subbandgap photo excitations produced by many-electron interactions
Authors: Chan Yang-Hao , Qiu Diana Y. , da Jornada Felipe H. , Louie Steven G.
Published: June 2021

Significance

Shift current, a bulk photovoltaic effect, arises from nonlinear light–matter interaction in a noncentrosymmetric crystal under continuous wave illumination. Although it is a promising mechanism for photocurrent generation without p–n junctions, the short-circuit current (which is related to the power efficiency of a solar cell device) is usually low. It is therefore important to understand the physics of the phenomenon and find materials with strong shift current conductivity. We calculate the shift current conductivity including excitonic effects in a real material (monolayer GeS) from first principles. We show that electron–hole interactions can dramatically enhance and qualitatively change shift current in reduced-dimensional materials. Our results indicate low-dimensional materials are promising candidates for next-generation photovoltaic devices with high efficiencies.
Men and women candidates are similarly persistent after losing elections
Authors: Bernhard Rachel , de Benedictis-Kessner Justin
Published: June 2021

Are women more likely to quit politics after losing their first race than men? Women’s first-time candidacies skyrocketed in the wake of the 2016 presidential election. Yet we have little sense of the long-term impact of this surge in women candidates on women’s representation writ large: Inexperienced candidates are more likely to lose, and women might be especially discouraged by a loss. This might make the benefits of such a surge in candidacies fleeting. Using a regression discontinuity design and data that feature 213,966 candidates across 22,519 jurisdictions between 1950 and 2018, we find that women who narrowly lose these elections are no more likely to quit politics than men who narrowly lose. Drawing on scholarship on women’s lower political ambition, we interpret these findings to mean that women’s decision-making differs from men’s at the point of entry into politics—not at the point of reentry.
Preferences for nutrients and sensory food qualities identify biological sources of economic values in monkeys
Authors: Huang Fei-Yang , Sutcliffe Michael P. F. , Grabenhorst Fabian
Published: June 2021

Significance

Preferences for foods high in sugar and fat are near universal and major contributors to obesity. Additionally, human food choices are sophisticated and individualistic: we choose by evaluating a food’s nutrients and sensory features and trading them against quantity and cost. To understand the mechanisms behind human-like food choices, we developed an experimental paradigm in which monkeys chose nutrient rewards offered in varying quantities. Resembling human suboptimal eating, the monkeys’ fat and sugar preferences shifted their nutrient balance away from dietary reference points. Formally defined economic values for specific nutrients and food textures explained the monkeys’ preferences and individual differences. Our findings show how human-like preferences derive from biologically critical food components and open up investigations of underlying neural mechanisms.
Strong evidence for the continued contribution of lead deposited during the 20th century to the atmospheric environment in London of today
Authors: Resongles Eléonore , Dietze Volker , Green David C. , Harrison Roy M. , Ochoa-Gonzalez Raquel , Tremper Anja H. , Weiss Dominik J.
Published: June 2021

Significance

Lead is a highly toxic element, and low-level environmental lead exposure remains a prime concern due its effects on neurodevelopment in children. It provides a well-researched example of the impact of human activities on environmental quality and the effectiveness of mitigation policies. Using recent and historical data on lead isotopic composition in London airborne particles, we show strong evidence that sources have not changed substantially since the ban in 1999 of leaded gasoline, the main source of environmental lead during the 20th century, suggesting that historical gasoline-derived lead remains an important source of lead in the urban environment due to its persistence and effective remobilization. Novel abatement policies need to be considered if this cycle is to be interrupted.
Dynamic innate immune response determines susceptibility to SARS-CoV-2 infection and early replication kinetics
Authors: Cheemarla Nagarjuna R. , Watkins Timothy A. , Mihaylova Valia T. , Wang Bao , Zhao Dejian , Wang Guilin , Landry Marie L. , Foxman Ellen F.
Published: June 2021

Initial replication of SARS-CoV-2 in the upper respiratory tract is required to establish infection, and the replication level correlates with the likelihood of viral transmission. Here, we examined the role of host innate immune defenses in restricting early SARS-CoV-2 infection using transcriptomics and biomarker-based tracking in serial patient nasopharyngeal samples and experiments with airway epithelial organoids. SARS-CoV-2 initially replicated exponentially, with a doubling time of ∼6 h, and induced interferon-stimulated genes (ISGs) in the upper respiratory tract, which rose with viral replication and peaked just as viral load began to decline. Rhinovirus infection before SARS-CoV-2 exposure accelerated ISG responses and prevented SARS-CoV-2 replication. Conversely, blocking ISG induction during SARS-CoV-2 infection enhanced viral replication from a low infectious dose. These results show that the activity of ISG-mediated defenses at the time of SARS-CoV-2 exposure impacts infection progression and that the heterologous antiviral response induced by a different virus can protect against SARS-CoV-2.
Symmetric and asymmetric structural evolutions of Te isotopes across the N = 82 shell closure *
Authors: Jiang Hui , Zhou Yi-jie , Lei Yang , Shen Jia-Jie , Bao Man
Published: June 2021

Systematic calculations of low-lying energy levels,

transitions, and g factors of even-even tellurium isotopes with mass numbers from 128 to 140 are performed via the nucleon-pair approximation (NPA) of the shell model with phenomenological multipole-multipole interactions. An optimal agreement is obtained between the calculated results and experimental data. The yrast band structures of nuclei below and above the

shell closure are compared and discussed. In particular, the evolutionary differences of

values and

factors, with respect to the symmetry of

, are attributed to the dominant contribution differences in neutron and proton excitations, respectively.
Primary thermometry at 4 K, 14 K, and 25 K applying dielectric-constant gas thermometry
Authors: Gaiser Christof , Fellmuth Bernd
Published: June 2021

This short note is a supplement to the paper ‘Primary thermometry from 2.5 K to 140 K applying dielectric-constant gas thermometry’ (2017 Metrologia
54 141–7). It deals with thermodynamic temperature measurements at the boiling point of the heavy isotope of helium (4He, 4 K) and the triple points of hydrogen (14 K) and neon (25 K). This is of special interest because recent data published in this temperature range have an unexpectedly large spread. The results presented in this short note show that the International Temperature Scale of 1990, ITS-90, is thermodynamically correct at 4 K and 14 K, but too high by about half a millikelvin at 25 K. Furthermore, care is given to two aspects of dielectric-constant gas thermometry in the low-temperature range. First, dielectric-constant gas thermometry can be applied for practical primary thermometry. The measurement of only one isotherm in one day yields a temperature value with an uncertainty order of a few tenths of a millikelvin. Second, the use of recent ab initio values for the virial coefficients of helium as a measuring gas can reduce the efforts significantly. Even one data pair of pressure and dielectric constant can yield a thermodynamic temperature value of uncertainty less than a factor of two larger compared to the uncertainty of the usually used fit evaluation. For 4 K and 25 K, the achieved final uncertainty for T is still larger than the realization uncertainty of T
90. Thereby in the case of 14 K, both uncertainties are comparable.
Simultaneous decoding of cardiovascular and respiratory functional changes from pig intraneural vagus nerve signals
Authors: Vallone Fabio , Ottaviani Matteo Maria , Dedola Francesca , Cutrone Annarita , Romeni Simone , Panarese Adele Macrí , Bernini Fabio , Cracchiolo Marina , Strauss Ivo , Gabisonia Khatia , Gorgodze Nikoloz , Mazzoni Alberto , Recchia Fabio A , Micera Silvestro
Published: June 2021

Objective. Bioelectronic medicine is opening new perspectives for the treatment of some major chronic diseases through the physical modulation of autonomic nervous system activity. Being the main peripheral route for electrical signals between central nervous system and visceral organs, the vagus nerve (VN) is one of the most promising targets. Closed-loop VN stimulation (VNS) would be crucial to increase effectiveness of this approach. Therefore, the extrapolation of useful physiological information from VN electrical activity would represent an invaluable source for single-target applications. Here, we present an advanced decoding algorithm novel to VN studies and properly detecting different functional changes from VN signals. Approach. VN signals were recorded using intraneural electrodes in anaesthetized pigs during cardiovascular and respiratory challenges mimicking increases in arterial blood pressure, tidal volume and respiratory rate. We developed a decoding algorithm that combines discrete wavelet transformation, principal component analysis, and ensemble learning made of classification trees. Main results. The new decoding algorithm robustly achieved high accuracy levels in identifying different functional changes and discriminating among them. Interestingly our findings suggest that electrodes positioning plays an important role on decoding performances. We also introduced a new index for the characterization of recording and decoding performance of neural interfaces. Finally, by combining an anatomically validated hybrid neural model and discrimination analysis, we provided new evidence suggesting a functional topographical organization of VN fascicles. Significance. This study represents an important step towards the comprehension of VN signaling, paving the way for the development of effective closed-loop VNS systems.
Identification of COVID - 19 from Chest CT Images using a Deep Neural Network with SVM Classification
Authors: Akshitha B , Arthi M , Brindha R , Sandhya G
Published: June 2021

Coronavirus is a quickly spreading viral illness that taints people; however, creatures are likewise to be contaminated because of this infection. The day-by-day life of people, their wellbeing, and the economy of a nation are influenced because of this lethal viral infection. A clinical investigation of COVID-19 contaminated patients has demonstrated that these kinds of patients are generally tainted from lung disease in the wake of interacting with this sickness. Chest X-beams (i.e., radiography) and chest CT are a more viable imaging strategy for diagnosing jump related issues. All things considered, a significant chest X-beam is a cheaper cycle in contrast with chest CT. Yet chest CT has more degree of accuracy. Profound learning is the best method of AI, which gives valuable examination to contemplate a lot of chest CT pictures that fundamentally affect the screening of COVID-19. This type has taken the Physician Assistant (PA) perspective on chest CT filters for Coronavirus influenced patients just as solid patients. After tidying up the pictures and applying information increase, the proposed system utilized profound learning-based SVM models and analyzed their exhibition.
Lifetime Prediction of Lithium-Ion Battery Using Machine Learning For E-Vehicles
Authors: Venugopal D , Pranav V Sharan , Lakshmi B Swathi , Vishnu K
Published: June 2021

A life cycle of battery with long testing time and without contact measurement devices will be applicable for industrial applications. To this problem, the solution for potential will be provided by the combined technique of supervised learning and infrared thermography. The focus of the research will be on machine learning techniques. Artificial neural networks (ANNs) and support vector machines (SVMs) are used in conjunction with thermography to estimate the life cycle of lithium ion polymer batteries. The capturing of infrared images at 1 frame per minute and charging of 70 minutes followed by the discharging of 60 minutes for 410 cycles. For ANN and SVM models the input nodes of charging or discharging use the surface temperature profiles. The input will be in thermal profile for the result. Under 10 minutes of testing time, we can estimate the current life cycle of a studied cell with an error of less than 10%. In SVM the accuracy will be similar while comparing with ANN but the testing time will be longer.
Study of the noise sources of an UAV with a two-stroke engine and shrouded propeller
Authors: Moshkov P A , Samokhin V F , Yakovlev A A
Published: June 2021

The widespread use of unmanned aerial vehicles poses the task of ensuring their low noise. To solve the problem of designing low-noise unmanned aerial vehicles, it is necessary to have data on the structure of the sound field of various unmanned aerial vehicles and their main noise sources. The results of an acoustic characteristics study of an unmanned aerial vehicle are presented. Its power plant includes a two-stroke piston engine and 4-bladed shrouded pusher propeller. The tests were performed in a wind tunnel at different speeds of the incident flow and different power conditions of the power plant. The dominant source of drone noise is a two-stroke piston engine. The propeller contribution is observed in the second and fourth tones in the radiation spectrum.
Modification of the Cu-Zr bronze surface by exposure to powerful UV laser pulses
Authors: Malinskiy T , Mikolutskiy S , Rogalin V , Khomich Yu , Kaplunov I
Published: June 2021

The laser pre-treatment of Cu-Zr alloy surface for diffusion welding, which is used in the aerospace industry for joining dissimilar materials, has been investigated. The effect of a nanosecond UV laser pulse on the surface of Cu-Zr alloy samples was studied. It was found that at a pulse energy density E ∼ 0.2-1 J/cm2 pre-ablative microscopic effects of mainly thermal nature were observed in the metal, also there were uplifts of material in the irradiated zone. The surface profile of the sample in the irradiated zone corresponds to the energy distribution of the laser beam. Significant deformations occurred in the crystal structure of the surface layer, and an irreversible configuration of the metal surface was created. At E ≥ 1 J/cm2 an optical breakdown with the formation of a plasma torch and with the appearance of a classical laser crater was observed. The arising erosion of the surface prevented registration of this effect. Microanalysis showed that the concentration of zirconium in the surface layer of the metal after exposure decreased.
Aircraft composite structures integrated approach: a review
Authors: Pogosyan M , Nazarov E , Bolshikh A , Koroliskii V , Turbin N , Shramko K
Published: June 2021

This paper presents a comprehensive program for modelling airframe structures made of composite materials using the finite element method. The purpose of this study is to apply the comprehensive approach to the creation of models in accordance with the main directions of numerical modelling. The “computational and experimental research pyramid” and its relationship with the complex modelling program are presented. Methods for calculating aggregates and structures using micromechanics, static, dynamic and resource strength methods are described, as well as the influence of the manufacturing cycle on the final performance of a product made of a composite material. This integrated approach allows one to optimize all the stages in the design process of the aircraft. Using this approach, one can replace part of the certification tests with modelling according to the “computational and experimental research pyramid”, which will reduce the cost of certification tests.
Optimal calibration plan for inertial measurement unit based on microelectromechanical system
Authors: Krylov A A
Published: June 2021

This paper is about the composition of scientifically substantiated calibration plan from the specific requirements for inertial measurement unit on microelectromechanical sensors. It is proposed to decompose the common problem into three tasks – converting implicit requirements to the explicit requirements with error components, determining of requirements by indirect parameters and finding direct parameter values, time limited calibration that have limits for full time. All these tasks may be presented as multi-criteria optimizations and be solved by numerical methods with some semi-analytical substitutions. Suggested methods are useful for composing an optimal calibration plan in conditions of ambiguous requirements, to estimate reaching accuracy, test volume and total calibration time. This approach offers the researcher a new look at the problem of balance between calibration accuracy and optimal use of resources.
Optimization of the mean-square approximation procedures for iterated Ito stochastic integrals based on multiple Fourier-Legendre series
Authors: Kuznetsov D F , Kuznetsov M D
Published: June 2021

The article is devoted to optimization of the mean-square approximation procedures for iterated Ito stochastic integrals of multiplicities 1 to 4 based on multiple Fourier-Legendre series. The mentioned stochastic integrals are part of strong numerical methods with convergence orders 1.0, 1.5, and 2.0 for Ito stochastic differential equations with multidimensional non-commutative noise. We show that the lengths of sequences of independent standard Gaussian random variables required for the mean-square approximation of iterated Ito stochastic integrals can be significantly reduced without the loss of the mean-square accuracy of approximation for these stochastic integrals.
Technique of constructing a measuring base for determining the azimuthal attitude of the dynamic test-bench Actidyn “ST2356C”
Authors: Zimin R , Veremeenko K
Published: June 2021

Calibration of inertial sensors is one of the most important tasks in the development of inertial navigation systems. The solution to this problem is impossible without achieving the required level of accuracy of dynamic modeling test-benches used in their development. The paper describes a technique of constructing a measuring base for determining the azimuthal attitude of the precision dynamic test-bench. This techniques used industrial geodesy technologies for providing ability to calibrate all major types of modern inertial measuring units in a wide temperature range. The azimuthal attitude determining is based on measuring the angular attitude of the mirror placed on the test-bench’s turntable by an autocollimation measurements technique by using a high-precision reflectorless total station, the coordinates of which are determined by rangefinder-goniometric measurements to reflectors with known coordinates, mounted on the room’s walls. The calculation results shows that proposed technique of constructing a measuring base allows to ensure the measurement accuracy for carrying out research and calibration of highly accuracy inertial measuring systems.
The Semi-Markov model of operation and maintenance of gas analytical system
Authors: Bobkov V , Kanishchev O , Men’shova I
Published: June 2021

Gas analytical systems are one of the key elements for the safe operation of airports and ground airspace infrastructure facilities where there is a risk to life or property caused by the possible combustible gases leaks. The gas analytical systems provides safety operation of airspace infrastructure facilities through the early detection of combustible gases and the issuance of warning signal; therefor the gas analytical systems is imposed high operational reliability requirements ensured by an optimal maintenance strategy. Known methods of maintenance management could not consider operation features and gas analytical systems structure complexity therefore increase cost of maintenance of airspace infrastructure facilities. The developed semi-Markov model of operation and maintenance of gas analytical systems, which takes into account the frequency and duration of control, the intensity of operation, the reliability of components, quantity of the spare parts and the gas analytical systems complexity makes it possible to design optimal maintenance strategy and therefore to reduce the cost of maintenance of ground airspace infrastructure facilities by reducing insupportable wear out of gas analytical systems and to reduce capital expenditures by excluding an excessive amount of the spare parts.
Improvement of projection-based LiDAR data segmentation algorithms using object-contextual representations
Authors: Stokolesov M , Yudin D
Published: June 2021

Nowadays self-driving cars and such unmanned aerial vehicles as drones are one of the most actively developed technologies, where machine learning algorithms play an irreplaceable role especially in the perception problem, which is the context of this research. To be applicable in self-driving cars and especially drones such algorithms should not only have good output quality, but also be real-time. For this reason, in the case of LiDAR data segmentation problem we pay special attention to algorithms that are based on point cloud projections because of their speed superiority over other heavy algorithms that process input point cloud directly. The main drawback of projection-based algorithms is their lower segmentation accuracy, so in this paper we show that it can be improved by integrating contextual representation module inside segmentation algorithm architecture. In our work we consider SalsaNext as a segmentation algorithm and OCR as a context representation module because these methods are among the highest in the corresponding datasets’ leaderboards. We provide results from quantitative evaluation on the Semantic-KITTI dataset, which demonstrate that the proposed SalsaNext modification gives 6.2% mean intersection over union metric improvement with no speed reduction.
Engineering of modernization of high technology products based on the concept of strategic risk
Authors: Burdin S , Moskvicheva N
Published: June 2021

The analysis showed that the most important results of the Aviation Industry Development Strategy are: an increase in the share of Russian manufacturers of aviation products in the world market; reorientation of the production of aviation industrial complex to the innovative segment of the global market. The aim of the study is to develop an engineering mechanism for the modernization of science-intensive products of the aviation industry. In accordance with this, a method is proposed for assessing the strategic risk of high technology products, a model for assessing the effectiveness of modernization of high technology products based on the concept of strategic risk as defining elements of the engineering process in the aviation industry. The practical implementation of the model is carried out.
Determination of the composite’s representative volume for longitudinal tensile test simulations
Authors: Turbin N , Kalutskiy N
Published: June 2021

In this study the proper size of the composite material’s representative volume element is addressed. Longitudinal tensile test simulations are conducted for a range of sizes and several variants of material models for matrix, fibre and interface. It is found, that matrix and interface degradation with prescribed properties do not influence the value of failure engineering stress for the cell in comparison with model, where only fibre damage model is set, and the adequate size of the cell is shown to be 80 µm. In contrast, variant contained stochastic fiber strength distribution shows different value for engineering failure stress and strain and suggests larger size of the material cell for simulations. Received results might be useful for accurate micromechanical modelling of material testing.
Attitude determination in integrated GNSS-inertial navigation systems in information and measurement insufficiency conditions
Authors: Zharkov M V , Veremeenko K K , Kuznetsov I M , Pronkin A N
Published: June 2021

The article presents the attitude determination algorithm for multi-antenna global navigation satellite and inertial integrated navigation system operating under information and measurement insufficiency conditions. The information and measurement insufficiency conditions are understood as the impossibility of the inertial system alignment on a fixed base and the absence of a redundant number of satellites to resolve the carrier phase integer ambiguity. The ability of the navigation system to operate in such conditions is achieved by combining several existing attitude determination methods and using the new method of attitude determination using ambiguous satellite phase measurements and absolute angular rate measurements. The hardware-in-the-loop simulation results using a 2-axis motion simulator and microelectromechanical systems inertial sensors are presented. The results confirm the efficiency of the proposed approach to the design of the navigation system algorithm.
Research and optimization of axial gas forces in turbines of turbojet bypass engines with afterburner combustion chamber
Authors: Malinovsky I M , Nesterenko V G , Ivanov I G
Published: June 2021

The paper presents the results of research and analysis of the efficiency of the power systems of the rotor of the gas generator of modern bypass engines with an afterburner. It was revealed that the gas axial forces, which are the difference between the axial forces of the rotors of the high-pressure compressor and its turbine, acting on the front angular contact bearing of the gas generator, can be significantly reduced in order to increase their reliability and service life.
Methods for flexibility determination of bolted joints: empirical formula review
Authors: Eremin V , Bolshikh A , Koroliskii V , Shelkov K
Published: June 2021

In this work, a comparative analysis of existing methods for determining the compliance of mechanical joints such as ‘composite-composite’ and ‘composite-metal’ is performed. Polymer composite materials are widely used in modern aircraft industry. As a result, it is necessary to take into account the characteristics of joints of composite aggregates with composite and metallic ones. Considering the compliance of connections in the global finite element models of structural units of aircraft allows increasing the accuracy of calculations. The use of empirical formulae can significantly reduce time and labour costs in calculating the compliance of bolted connections for use in global finite element models. In this paper we review and analyse the existing empirical dependencies. Calculation of rigidity and compliance of single-shear ‘composite-composite’ and ‘composite-metal’ joints by finite element method for small, medium and large membrane thicknesses is carried out, and the results are compared with the calculations using empirical formulae. As a result of the analysis for medium and small thicknesses it is proposed to determine the value of bolted joint flexibility by the empirical formula Boeing 1, and for large thicknesses of connecting membranes it is proposed to use empirical formula Huth.
Development of a methodology of estimating limits of oscillations of optical system of photoelectric rotary encoders
Authors: Korolev I , Chekin A
Published: June 2021

The development of optical sensors with rotating mechanism requires estimation of oscillations limits. Although some work has been done on to linear encoders, there’s no information on such approaches related to rotary encoders. This manuscript proposes a computational approach of estimating oscillations limits of optical systems of rotary encoders. The approach is based on machine computations of waveforms modified by shifting position of one of discs, and rotates not around main axis of optical system. For estimations of oscillations during computations, one of optical discs translated against optical axis of optical system to perform occlusions, accounting differences in light distribution with oscillations presented. As the result of applying of methodology, computer program described and tested to calculate limits of hypothetical optical system, as well as its predictions were confirmed by comparison with behavior of real rotary encoder. This data was achieved with fewer computations, compared to classical calculation methods of light propagation. Developed methodology allows creating computer programs for estimating limits of oscillations within reasonable timeframe.
Study of BPF pressure pulsations reduction in centrifugal bladed machines using splitters
Authors: Klimenko D , Kondratov A , Timushev S , Li J
Published: June 2021

Presence of intensive pressure pulsations and noise on blade passing frequencies is a characteristic feature of all types of centrifugal bladed machines including pumps. Under definite conditions pressure pulsations can reduce the pump reliability and life cycle. High level of tonal noise can be inappropriate due to ecological requirements. The paper is devoted to the study of application of splitters for reduction of pressure pulsations in centrifugal pumps. 2D and 3D numerical methods are used in the study. Initial computational tests were performed with a two-dimensional formulation for a centrifugal pump with a simple volute using 2D discreet vortex method for the impeller flow and 2D acoustic-vortex approach for pressure pulsations prediction. 3D unsteady flow computations of an air model of the centrifugal pump are undertaken with the impeller having splitters. Calculations of pressure pulsations show that the use of additional blades reduces the amplitude of the first harmonic of blade passing frequency by more than three times compared to the design without splitters. It correlates with flow parameters distribution along the impeller outlet diameter that has less nonuniformity and a more balanced vorticity profile. Application of splitters reduces the amplitude of pressure pulsations by a factor of 3.
Prediction of the structural state in a wheel forging based on computer modeling
Authors: Ovchinnikov A V , Pchelnikov A V
Published: June 2021

The landing gear of any flying vehicle is a unit of increased responsibility. The entire load during take-off and landing is perceived by the wheels of the landing gear. The reliability of aircraft wheels is determined, among other things, by the distribution uniformity of the structure and mechanical properties over their volume. This work represents a method for predicting the structural state in stamped forging of an aluminum alloy wheel included in the chassis of a small bomber. Based on the simulation results (deformation temperature and deformation rate), the cause of grain growth in the area of the wheel rim is determined. Using the structural state diagrams of Vainblat Yu M. It is shown that a region with coarse grains in the rim is formed due to local recrystallization during heating for quenching. Based on analysis of temperature-speed conditions in coarse-grained area, stamping modes are proposed with stepwise reduction of deformation rate at the final stage of the process, which excludes recrystallization.
Influence of adhesive bond line thickness on joint strength of composite aircraft structures
Authors: Kostin V , Nasonov F , Zinin A
Published: June 2021

Methods for assessing the effect of the thickness of the adhesive layer in the adhesive joint of thin-walled composite structural elements on the strength of the entire joint are considered; a critical analysis of existing theoretical methods for predicting the strength of adhesive joints is given. The contradiction between the theoretical estimates of the effect of the adhesive thickness on the strength and the results of experiments and practical experience in the use of adhesive joints of composite panels is established. It is revealed that the most effective methods for predicting the load-bearing capacity of adhesive joints are energy models of fracture mechanics based on the intensity of the release of fracture energy and the formation of a pre-fracture zone in the adhesive layer. Assuming the determining role of changes in the size and shape of the initial fracture zone depending on the thickness of the adhesive layer, the results of the prediction of the strength of the adhesive joint are compared with experimental data.
Analysis of the geometric parameters influence on the labyrinth seals performance
Authors: Androsovich I , Borovikov D , Siluyanova M
Published: June 2021

One of the ways to improve the modern gas turbine engines efficiency is to increase the efficiency of its components. An increase in the gas turbine engine components efficiency may be achieved by reducing air leaks by the seals usage. It is possible to achieve a reduction in air consumption through the seal, including off-design operation conditions, by using modern methods of computational fluid dynamics simulations. One of the possibilities of modern computational fluid dynamics methods is to analyze a simultaneous effect of the large number of variable design parameters. Performance of different labyrinth seals type is analyzed. Direct-flow labyrinth seal is chosen as most common in jet engine design due to its properties. Geometric parameters influences are defined. Optimization resulted in a labyrinth seal configuration that achieves a 20% reduction in seal mass flow. A comparison of the mass flow characteristics of the original and the optimized seal showed that the optimized seal provides reduced mass flow over a wide range of pressure ratios. The results obtained lead to the conclusion about geometric parameters influence on the mass flow and the effectiveness of labyrinth seals optimization to reduce air leaks.
Mathematical modeling in cognitive process research
Authors: Korzhuk N L , Kh Melnikov A , Indyukhin A F , Indyukhin A A , Korzhuk V N
Published: June 2021

There was proposed a method for studying and mapping the cognitive activity of the brain. The experiment simulates a flight situation: the appearance of an image, recognition, a motor act (inner speech). Electroencephalogram was recorded with cognitive load. Two figures are presented on the laptop screen- a circle and a square. At the moment of presentation of the stimulus, the matching device sends a synchronizing pulse to one of the inputs of the electroencephalogram amplifier. The subject mentally names a figure with a larger area. A selective filter system suppresses background activity. The resonant frequencies of the filters are changed to reveal a single cognitive response to a stimulus. The parameters of the model are individual for each subject. There was developed a model of a diagnostic device. The results obtained for the “circle” and “square” figures coincide at time interval corresponding to the work of the sensory visual system, but they differ at the stage of internal speech, which corresponds to pronouncing a longer word by the syllables. These results demonstrate the effectiveness of modeling in studies on the localization of the cognitive process and the diagnosis of neurological disorders.
Study of the effect of the elastic modulus of ribs on the stress-strain state of a composite mesh compartment
Authors: Repinsky V V , Bakulin V N
Published: June 2021

Modern fiber composites have extremely high specific strength and stiffness, significantly exceeding the corresponding characteristics of traditional metal structural materials. In the present work, the effect of the elastic modulus of circular and spiral ribs on the stress-strain state of a composite mesh compartment with cutouts reinforced with bezels investigated. For the calculations, the finite element method is used, which makes it possible to naturally consider the cutouts, stepwise varying thicknesses, various kinds of boundary conditions, and loads. The computational model of the composite lattice structure consisting of ribs is a finite element model constructed from beam elements. The parameters of the stress-strain state of a composite mesh compartment with notches reinforced by edgings are determined. The graphical dependences of the values of maximum stresses in the ribs and sheathing on the value of the modulus of elasticity are presented for the first time. The analysis of the obtained results carried out, which makes it possible to develop recommendations for an informed choice of carbon fabric types with different physical and mechanical characteristics for manufacturing the spiral and ring ribs, as well as the skin of the designed composite mesh compartments.
A fine-grained teaching activity to establish conceptual coherence in introductory physics concepts and representations
Authors: Ferreira A , Lemmer M
Published: June 2021

The sequence of representations used to introduce new knowledge and the context in which this is done is critical to both effectively build on prior knowledge and establish conceptual coherence in physics. Ongoing reports indicate that current teaching activities fail address student difficulties to obtain conceptual understanding and-coherence between relevant physics representations and concepts. There is a need for fine-grained topic specific multiple representational teaching activities to enhance coherence in physics knowledge. In this paper we present a teaching activity for undergraduate physics, built on using motion diagrams to specifically relate the concepts and representations in kinematics, in particular for the concept of free fall. The teaching activity follows a conceptual qualitative approach to teaching kinematics concepts and is informed by the results of a broader Design Based Research study. In the teaching activity the concept of acceleration is introduced qualitatively as the net force to mass ratio followed by drawing motion diagrams to visualize the motion of the objects in free fall. The motion diagrams are implemented to support conceptual qualitative interpretation of mathematical representations such as graphs and equations, to enhance transfer of knowledge between representations and coherence between relevant concepts and representations. The contribution of this research lies in presenting an argument for a conceptual qualitative approach to teaching introductory mechanics and introducing a teaching activity based on the value offered of including motion diagrams in the teaching activity to enhance coherence between physics representations and between physics concepts.
Misconceptions in mechanics and their elimination
Authors: Kuczmann Imre
Published: June 2021

Misconceptions are beliefs that contradict accepted scientific knowledge but they are seemingly supported by common-sense arguments. By testing misconceptions, we have deduced that they are also related to the structure of knowledge. Some basic elements of the incomplete knowledge structure have been identified, which promote the root of misconceptions to be persistent. Based on recognizing and eliminating these shortcomings, distinct guidance for the prevention or overcoming of misconceptions is proposed.
The value of a complex physical experiment virtualization in the strategy of improving the educational process
Authors: Gabdullina A T , Skudra A , Tuimebekova A T , Fermakhan K , Zhukeshov A M , Amrenova A U , Yengay V
Published: June 2021

It has now been established that the modern educational process is becoming more effective when using interactive, multimedia-rich educational resources that provide active teaching methods. The best way to meet these requirements are educational resources and virtual reality systems. An example of such electronic resources is virtual laboratory work, which can simulate the behavior of real-world objects in a computer-based educational environment and help students learn new knowledge and skills. This is relevant and already mandatory in the study of scientific and natural disciplines, such as chemistry, physics, mathematics, computer science and their combinations. Virtual laboratories contribute to increasing visibility, interactivity, as well as the formation of students’ cognitive and creative activity. In this regard, the development of a virtual model of a physical experiment on laboratory equipment that has a real analogue was the goal of this work. The paper presents data on the creation of the experimental setup interface developed in the laboratory of a pulsed plasma accelerator of Al-Farabi Kazakh National University, called the vacuum-arc accelerator (hereinafter VAA-1). At this installation, experiments are carried out to obtain coatings from various materials on a metal base from structural materials in order to create a protective and multifunctional layer on its surface.
Examining Students’ Interest in Physics at Second Level in Ireland
Authors: O’Neill D , Mcloughlin E
Published: June 2021

This study examines students’ interest in physics within the culture and context of the Irish education system, at both lower and upper second level. In Ireland, the majority of students (aged 12-15 years) complete an integrated science curriculum at lower second level that encompasses learning outcomes across the disciplines of physics, chemistry, biology and earth and space. Students can choose what subjects they continue with at senior cycle and typically, 13-14% of students (aged 15-18 years) continue to study physics. This study reports on the student’s interest in physics and presents collated responses from 563 lower second level science students and 142 upper second level physics students. The findings of this study denote the differences between males and females interests in studying Physics at each level and in particular, highlight the effect that school type has on females’ interest in physics.
Learning motion concepts using Augmented Reality Active Learning (AnReAL) activities
Authors: Rosi T , Onorato P , Oss S
Published: June 2021

Active learning and discovery-based laboratory curricula for the understanding of kinematics using motion sensors have extensively been studied in Physics Education Research for more than thirty years and provided strong evidence of their usefulness in terms of students learning and retention. More recently, activities based on video analysis software have also been developed and have become an important part of Physics Education Research. In this work we present a setup based on Virtual Reality (VR) headsets that may be used both for activities that are currently based on motion sensors and also for motion tracking. Our setup is based also on cameras that can be attached to the headsets in order to achieve an Augmented Reality experience. While VR headsets are mainly sold as gaming devices, they can be very interesting for Physics Education active learning activities: we called such an activity an Augmented Reality Active Learning (AnReAL) activity. As it will be shown, many curricula based on motion sensors or on video tracking can almost automatically be translated into AnReAL ones, while also being open for many new opportunities. In fact, following the emerging theory of Embodied Cognition, Virtual and Augmented Reality setups such as the presented one could prove to be very beneficial for information retention.
Web 2.0 applications as the tools of motivation in secondary physics education
Authors: Takátsné Lucz I
Published: June 2021

The aim of this study is to introduce some effective methods of integrating educational web 2.0 apps into Physics lessons, to share some experience and ideas how they can be used to support learning and make students more active in the learning process. This collection of apps focuses on the most popular activities of the students (using social media, playing online games etc.) A short insight will be given into the procedure how these modern techniques can foster the students’ creativity, develop their collaboration skills, give opportunity to deal with differentiated learning problems and, last but not least, change the students’ attitude towards learning Physics.