bluuebunny/crossref_metadata_2025_split huggingface dataset:
CMB lensing power spectrum estimation without instrument noise bias
Authors: Madhavacheril Mathew S. , Smith Kendrick M. , Sherwin Blake D. , Naess Sigurd 
Published: May 2021

Abstract
The power spectrum of cosmic microwave background (CMB) lensing will be measured to sub-percent precision with upcoming surveys, enabling tight constraints on the sum of neutrino masses and other cosmological parameters. Measuring the lensing power spectrum involves the estimation of the connected trispectrum of the four-point function of the CMB map, which requires the subtraction of a large Gaussian disconnected noise bias. This reconstruction noise bias receives contributions both from CMB and foreground fluctuations as well as instrument noise (both detector and atmospheric noise for ground-based surveys). The debiasing procedure therefore relies on the quality of simulations of the instrument noise which may be expensive or inaccurate. We propose a new estimator that makes use of at least four splits of the CMB maps with independent instrument noise. This estimator makes the CMB lensing power spectrum completely insensitive to any assumptions made in modeling or simulating the instrument noise. We show that this estimator, in many practical situations, leads to no substantial loss in signal-to-noise. We provide an efficient algorithm for its computation that scales with the number of splits m as 𝒪(m2) as opposed to a naive 𝒪(m4) expectation.
Niobium carbide (Nb2C) MXene as a saturable absorber to assist in the generation of a wavelength tunable passively Q-switched fiber laser
Authors: Ahmad Harith , Yusoff Norazriena , Albaqawi Hissah Saedoon , Reduan Siti Aisyah , Thambiratnam Kavintheran 
Published: May 2021

Abstract
Niobium carbide (Nb2C), a new member of the MXene family, is proposed as a potential saturable absorber (SA) material. Stable Q-switched pulses were established in the C-band wavelength region upon employing a Nb2C/PVA film-based SA in the erbium-doped all-fiber ring cavity. The generated EDF laser operated at a wavelength of 1558.73 nm with a corresponding 3 dB bandwidth and signal-to-noise ratio of 2.8 nm and 53.8 dB. A maximum pulse repetition rate and pulse energy of 75.19 kHz and 15.63 nJ were observed at a maximum pump power of 224.5 mW. Interestingly, the emission spectra can be continuously tuned across 44 nm ranging from 1522.32 nm to 1566.07 nm by controlling the tunable band pass filter that has been introduced in the laser cavity. Our findings reflect the feasibility of using Nb2C as an excellent broadband SA material that underpins new opportunities for photonic technology and other potential applications in nonlinear optics.
Mathematical modelling of a gas turbine engine based hybrid propulsion system for regional airplanes
Authors: Ravikovich Y A , Agulnik A B , Kholobtsev D P , Borovikov D A 
Published: May 2021

Abstract
The work is a study of light multi-purpose aircraft hybrid propulsion advantages. A comparison of propulsion system dynamics and the integrated flight performance in the cases of turbo-prop and a hybrid turbo-prop propulsion usage has been carried out. Required battery parameters are calculated for usage of hybrid mode during a flight mission and for emergency landing on the hybrid propulsion electrical component. The calculation results showed that a hybrid propulsion system may have a longer operating life, lower fuel consumption during non-cruising flight modes, and the possibility of landing in case of gas turbine failure.
A Dovetail Joint for a Segment Permanent Magnet on a Rotor
Authors: Ilyasov R , Dezhin D 
Published: May 2021

Abstract
Specific weight-power parameters (kW/kg, (kW/dm3)) of rotary electric machines depend on the rotational speed of the rotor. Bandage in high-endurance titanium [1] or carbon fiber-based nonmagnetic materials is used conventionally to enhance the rotor strength of magnetoelectric excitation high-speed electric machines. Eddy currents induced by tooth harmonics are seen as a major flaw in weighty titanium bandage, while a widened mechanical gap between the rotor and the stator is the principal shortcoming of nonmagnetic bandage, as it reduces magnetic induction values within the gaps. This article discusses a way to increase the rotor top rotational speed (the radial speed) through a dovetail permanent magnet joint solution without using additional titanium or carbon fiber bandage.
Thermodynamic parameters optimization of an aviation three-shaft turbofan engine with an intercooler and a recuperator under flight condition
Authors: Omar H H , Kuz’michev V S , Tkachenko A Y 
Published: May 2021

Abstract
The use of heat recovery in turbofan engines to improve their efficiency is not so obvious. Installing a recuperator behind the turbine of the main engine duct to heat the air at the entrance to the combustion chamber, on the one hand, reduces fuel consumption, but on the other hand, leads to a decrease in the temperature at the entrance to the jet nozzle of the main duct, thereby reducing the gas flow rate from the nozzle and, consequently, the specific thrust and thrust of the engine as a whole. The installation of an intercooler for intermediate cooling of the air between compressors allows to reduce the net-work and power of the high-pressure compressor and increase the gas pressure behind the turbine, and, consequently, the speed, specific thrust, and thrust of the engine. However, the amount of possible gain in the efficiency of a turbofan engine due to heat recovery will depend on how well the parameters of the working process of the engine and heat exchanger are selected. And this can be done only by optimizing these parameters in terms of evaluating the efficiency of the engine in the aircraft system. The article presents the results of optimizing the parameters of the working process of three-shaft turbofan engines with an intercooler and a recuperator in the system of a passenger aircraft of the Boeing 737 MAX 7 according to such criteria as the total weight of the power plant and the fuel required for the flight, and the specific fuel consumption of the aircraft per ton-kilometer of the transported commercial load.
Modelling of aerodynamical interaction of the wing and propellers of a distributed propulsion system
Authors: Vlasov A V , Varyukhin A N , Brailko I A , Lebedev A O , Zakharchenko V S , Ovdienko M A 
Published: May 2021

Abstract
The paper describes a study of a distributed electric propulsion system impact on the aerodynamic performance of an aircraft wing. A semi-empirical method and CFD calculation method for prop blown wing influence on take-off and landing characteristic were considered and compared. Results of these methods are compared. Optimal location of a prop with leading edge of an airfoil in terms of maximize lift coefficient was obtained through the CFD method.
Aerodynamic analysis of the small-scaled centrifugal compressor for micro-turbojet engine applications
Authors: Sebelev A.A. , Tikhonov A.S. , Aleksenskiy V.A. , Shengals A.A. , Klyavin O.I. 
Published: May 2021

Abstract
This paper presents the results of an aerodynamic analysis of a small-scaled transonic centrifugal compressor for micro turbojet engine (TJE) applications. The analysis was conducted using a CFD model validated by experimental data collected for the gaged JetCat P200-RX micro-TJE. The loss coefficients of the impeller, vaned diffuser and deswirler were estimated for 4 design points corresponding to 70%, 80%, 90% and 100% rotation speeds to perform the loss balance diagram. The flow angle spanwise variation demonstrated an intensive flow separation zone at the top 25% of the vaned diffuser span due to the pressure shock appearance. It was shown that the main source of the losses in the investigated compressor is the deswirler due to non-optimal flow turning conditions. The diffuser loss coefficient was estimated as 0.18 at the compressor full load.
Impact of a thermally stratified energy source on the bow shock wave and aerodynamic characteristics of a body
Authors: Azarova O A , Kravchenko O V 
Published: May 2021

Abstract
This paper presents numerical modelling of a thermally stratified energy source’s effect on the supersonic flow past a body “double-wedge - plate”. A multiple generation of the Richtmyer-Meshkov instabilities was obtained. These instabilities cause almost complete destruction of the bow shock front inside the source area and form a new multi-vortex mechanism of affecting the streamlined body. The defining parameters of the effect of stratified and homogeneous energy sources with equal values of total energy are analysed. The possibility of a significant decrease in the temperature at the vertex of the double-wedge and in the average front surface temperature due to the redistribution of source energy between layers has been established.
Studying unsteady combustion processes that occur in an annular combustion chamber of a gas turbine engine
Authors: Morales M.Hernandez , Zubrilin I.A. , Gurakov N.I. , Kolomzarov O.V. , Makaryants G.M. , Sigidaev A.V. , Tarasov D.S. 
Published: May 2021

Abstract
When designing low-emission combustion chambers for gas turbine engines (GTE) and power plants, determining their tolerance to high-amplitude pressure oscillations during combustion is a challenging task. This paper proposes a modified instability criterion of combustion processes, which allows us to assess the influence of design and operating parameters on the amplitude of pressure oscillations. The comparison between the modified criterion and experimental data showed that for the volume-averaged estimation of the criterion, it is necessary to use the flame front region, defined by the value of the Progress Variable parameter of the FGM combustion model in the range of 0.3-0.7.
Developing a method of low cycle fatigue life prediction for large-sized parts based on testing equivalent samples and applying it when improving gas turbine engine critical parts
Authors: Pakhomenkov A V , Bukaty S A , Shmotin Yu N 
Published: May 2021

Abstract
This paper presents the methodology of LCF equivalent tests based on the application of test samples whose stress-strain state (SSS) is similar to the stress-strain state of the part in its critical zone by using the stiffness coefficient of the stress-strain state. Requirements for manufacture of test specimens have been defined. This method was successfully tested on the example of a gas turbine engine LPC disk. The method was also used to improve the design of disk / blade root connection which resulted in a 3-fold increase of low cycle fatigue life of the disk. Method of equivalent testing is intended for prediction of cyclic fatigue life of critical large-sized parts full-scale tests of which are not possible or economically feasible.
Reduction of the finite element model of a gas turbine engine rotor using CMS technique
Authors: Semenov S.V. , Nikhamkin M.Sh. , Sazhenkov N.A. 
Published: May 2021

Abstract
This paper is devoted to the problems of modeling the vibration behavior of rotors of gas turbine engines. The necessity of modeling their dynamic behavior is caused by their strong influence on the strength characteristics of the engine and its resource. The complexity of solving this problem lies in the fact that the design of modern gas turbine engines has many features that do not allow the use of only one-dimensional models, and the application of three-dimensional models requires a lot of computing resources. Thus, it is suggested to use methods of reduction of finite element models for solving the problems in three-dimensional statement. This paper uses the mode component synthesis (CMS) method to reduce the dimensionality of the rotor model. It also compares the speed of solving modal analysis tasks and determining critical frequencies using complete and reduced models. The quality of reduction is determined. Conclusions about the efficiency of the reduction technique aimed at solving rotor dynamics problems are made.
Influence of geometric deviations of the fan blade airfoil on aerodynamic and mechanical integrity
Authors: Ravikovich Yu , Kholobtsev D , Arkhipov A , Shakhov A 
Published: May 2021

Abstract
A technology for robust multi-criteria optimization of the fan blades with real deviations of airfoil geometry is proposed which includes simultaneously solving aerodynamic and mechanical integrity problems as well as balancing and arranging the blades in the row. In accordance with this technology, automated measurements of blades airfoil geometry (more than 1200 points) are used to automatically create a blade “cold” 3D model, meshing, and static and dynamic analysis of mechanical integrity. Then the model and mesh are automatically transformed in a “hot” condition and an aerodynamic analysis is carried out to estimate the measured geometry influence on fan parameters. Finally, arrangement of blades in the row is carried out based on static moments and aerodynamics analysis. The final stages of this technology are presented in this paper more detail.
Information flows of parallel computing of the distributed control systems of aviation engines
Authors: Tovkach S 
Published: May 2021

Abstract
The ongoing work on scientific and technical suggestions for 6th generation engines has been considered and the necessity for developing methods for constructing adaptive control of aircraft engines has been substantiated, which will allow, due to the flexible structure of the control system, to determine the number of adjustable parameters and the number of adjustable factors for the formation of engine control programs. The information flows of aircraft engine control systems have been analyzed using an example of a system with full responsibility of the FADEC type and a method for their parallel calculations is proposed, for the implementation of which it is necessary to develop a virtual channel model, a background stream generator, and a data parallelization method.
Experimental study of heat transfer inside a real scale innovative air solar collector
Authors: Sima C , Teodosiu C , Croitoru C , Bode F 
Published: May 2021

Abstract
The study is performed on a glazed transpired solar collector, investigating the effect of different distances between the glazing and the absorber (30, 50, 70, and 100 mm) for different airflow values. The results show that the best solution among the tested configurations is with 30 mm distance between the glazing and absorber, no matter what the air flow rate is. The efficiency of the GTC in this case is 16-19% higher for air flow rates around 100 m3/h, m2 and even 30-40% higher for air flow rates around 150-200 m3/h, m2 – compared to configurations with larger distance between the glazing and absorber.
Analysis of velocity and temperature fields inside an air solar collector – A numerical approach
Authors: Teodosiu C , Sima C , Bode F , Croitoru C 
Published: May 2021

Abstract
The numerical study is performed on a glazed transpired solar collector, investigating the effect of different distances between the glazing and the absorber (30 and 50 mm) for different airflow rates. The results show that the best solution among the tested configurations is using the 30 mm distance between the glazing and absorber, no matter what the air flow rate is. The efficiency of the glazed transpired solar collector (GTC) in this case is between 50%-61% for the range of airflow rates studied and higher with around 15% compared to configurations with larger distance between the glazing and absorber. The purpose of this study is to prove the efficiency increase due to pass-through elements disposals complementary with the passive components implementation, underlining the benefit of passive solar systems.
Review of the technologies for nitrates removal from water intended for human consumption
Authors: Matei A , Racoviteanu G 
Published: May 2021

Abstract
The goal of this paper is to review the technologies used for nitrate removal from water intended for human consumption. It also reviews the effects of nitrates on human health and the various legislative provisions in different states. The treatment technologies that will be detailed are: reverse osmosis, ion exchangers, biological denitrification and electrodialysis. For every technology, the following information will be provided: advantages, disadvantages, process performance and cost. Furthermore, there will also be examples of water treatment plants across the Globe that use these types of technologies for nitrate reduction.
Design considerations for an Archimedean screw hydro turbine
Authors: Dragomirescu Andrei 
Published: May 2021

Abstract
Archimedean screws have been used for centuries, but only for pumping water. In the last decades, a growing interest appeared to also use them as hydro turbines for electricity generation. While Archimedean screws are already well optimized for working as pumps, studies are still carried out to identify those parameters that assure the best performances when they operate as turbines. This paper proposes a simple yet efficient procedure for the design of an Archimedean screw operating as a turbine. The most important formulas proposed in the paper are those for calculating the outer diameter and the rotational speed of the screw. The condition imposed for finding the diameter is the maximization of the torque produced. The calculation of the diameter requires to estimate the volume of the water buckets that form between the blades of the screw. It is practically impossible to find an analytical formula for this volume, but a rough estimate can be found easily. This rough estimate is corrected afterwards based on regression of data available for turbines that already operate with good efficiencies. The rotational speed is then determined based on the condition that the rated discharge can run through the turbine operating at the rated speed.
Influence Of A Descentralized Ventilation System On The Indoor Air Quality Of A Primary School Classroom
Authors: Catalina T , Lungu C 
Published: May 2021

Abstract
The indoor air quality is one of the main factors influencing the comfort in a building. This subject has already been covered by several studies in the case of adult’s work environment. The research study is focused on the air quality in a primary school classroom and the children’s sensation related to interior comfort. In this article we will present the results of the air quality experimentations when using a ventilation system. The classroom is equipped with a heat recovery unit. In order to perform CO2, temperature and relative humidity (RH) measurements, we used ten portable measurement units. The sensors have been set in different spots of the classroom. The heat recovery ventilation unit had an important influence on the air quality when it was running. The observed result of this phenomenon was that the measures were homogeneously distributed in the classroom instead of being concentrated in different points. Moreover, it was found that with 17 m3/h/pers. the indoor CO2 concentration can be dropped below 1000 ppm. The last part of the experimental study was based on a survey with different question regarding air quality, temperature and noise.
Speed Control of the Direct Current Servomotor and the Stepper Motor with Arduino UNO Platform
Authors: Darie E , Pécsi R , Culcea M 
Published: May 2021

Abstract
Servomotors are special direct current or alternating current electric machines which have an adjustable rotational speed in a wide range, in both directions and which aim at moving a mechanical system along a trajectory in a prescribed time. Servomotors are used in various applications: robotics, machine tools with numerical control, aerospace technology, medical installations and others. Stepper motors are special synchronous machines that have a different construction than the classic one and are used in precision drive systems, with open loop such as: aircraft on-board equipment, timing and recording systems, electronics, office equipment, robotics industrial, etc. This paper experiences the speed control of a direct current servomotor, type SM-S2309S, with the help of the Arduino UNO platform, which is the simplest solution for the development of electronic applications. The study experiences also speed and step control of a stepper motor, type 28BYJ-48, with the Arduino UNO platform.
nZEB into the existing building fund as an affordable solution
Authors: Măgurean Ancuţa Maria 
Published: May 2021

Abstract
A holistic approach with high level of replicability and financial feasibility for the public existing fund of buildings is undertaken, in order to transform existent public buildings, that are serving communities, into nearly Zero Energy Buildings. Finding large scale solutions from both technical and financial point of view, to reduce energy consumptions and CO2 emissions for the existent building fund represents at this point a major challenge for all stakeholders. Several existent educational units (kindergartens, schools, high schools) from a city in Romania were analysed, in order to improve their energy efficiency and to transform the typical existent educational unit into nZEB. A framework package of technical solutions is proposed and the effect of its implementation is analysed, in terms of energy consumptions and CO2 emissions reductions. Economic analysis is undertaken, to identify the feasibility of the nZEB concept implementation. An alternative approach is analysed for public authorities, in order to transform groups of existent buildings, which are serving communities, into nZEB.
Identification of Key Performance Indicators related to the implementation of a hybrid energy supply system based on renewable energy sources
Authors: Tuţică D , Sandu M R , Pătraşcu R , Ionescu C 
Published: May 2021

Abstract
Complex energy systems need to evaluate their performance through the achievement of its own objectives but also by comparison with best practices. This can be realized by identifying the key performance indicators (KPI) that clearly monitor the progress towards project goals. The work focuses mainly on the identification and categorisation of KPIs through a quantitative approach for the case of implementation of a hybrid energy supply system into the existing district heating network of University Politehnica of Bucharest. The main results of the study show that two levels of KPI can be defined: technology specific and overall DHC system. If on the technology level, the approach is to use the specifics standards already existing for the main technologies, for the system level, little information is available and consequentially, a method for calculating separately the cooling and heating impact in terms of energy, environment, and economy is proposed.
Mixing Flow Characteristics in cylindrical tank
Authors: Danca P A , Băbuţanu C A , Bunea F , Nedelcu A 
Published: May 2021

Abstract
The characterization of the flow from mixing tanks equipped with different impeller models is used for optimizing mixing of working fluids. In this paper is presented a study on flow characteristic of two types of impeller immersed in a tank at different depths and with different rotational speed. Using PIV technique flow distributions for several mixing configurations are obtained. The experiment can be used to determine the still zones in the mixing tank and for the optimization of the mixing parameters.