bluuebunny/crossref_metadata_2025 huggingface dataset:
The impact of the Sino-US trade war on Chinese goods and digital trade from the perspective of the Internet
Authors: Wang Mengyao , Liu Lan
Published: May 2021

With the maturity of information technologies such as big data, blockchain, industrial Internet, and artificial intelligence, the Sino-US trade war continues to escalate.It can be predicted that after the Sino-US trade war in goods, a “digital trade war” may have begun quietly.On the one hand, the key to Internet issues is data governance rules, which are related to digital trade and digital economy, and are the key to future national competitiveness;on the other hand, the impact of the trade war on China’s trade in goods is also an issue that needs to be discussed.The article found through research that the negative impact of the Sino-US trade war on China is gradually showing. The scale of China’s trade import and export has shrunk, and a lot of trade opportunities have been lost.The prediction of “internet fragmentation” is becoming a reality.I analyzed the countermeasures to deal with the trade war from the aspects of conducting trade negotiations, expanding internal demand, and handling data governance issues.
Improvement of photoluminescence intensity and film morphology of perovskite by Ionic liquids additive
Authors: Shen Dongyang , Luo Chengzhao , Zheng Ronghong , Li Qinyi , Chen Yu
Published: May 2021

Metal halide perovskites have received much attention for their application in light-emitting diodes (LEDs) and solar cells in the past several years. Among them, 2D and quasi-2D perovskite with organic long-chain cations introduced have drawn significant attention. However, while improving wet and thermal stability, as the grain size becomes smaller, more defects introduced at the grain boundary and surface, resulting in the increase of non-radiative recombination is becoming the main problem which should be faced by 2D/quasi-2D perovskite materials. Here, we report a new strategy employing ionic liquid named 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide(EMB).By adding a small amount of ionic liquid to the precursor, the defect was effectively passivated and the photoluminescence intensity was increased by 11 times and the fluorescent lifetime was increased by about 1.5 times. The flatness of the prepared perovskite thin films has also been effectively improved.
Environmental Management and Development Strategy of Cross-border River Water Resources
Authors: Zhen Zhen
Published: May 2021

International Rivers pass through more than two countries, which makes it difficult to manage international rivers. Nowadays, the integration of world economic development determines the increasingly close cooperation between countries. The international river has become a hot area of economic development. How to rationally develop and utilize the international river and make it healthy and sustainable development is an important problem facing all countries. China is rich in cross-border river water resources. With the increasingly obvious economic status of cross-border river water resources, how to use cross-border river is an urgent problem. Combined with the distribution characteristics of cross-border rivers in China, this paper discusses the strategic significance of cross-border river development and utilization for national development, combs the current situation of cross-border river development and utilization, and puts forward corresponding measures for cross-border river development strategy, which has reference value for solving the problems caused by cross-border river development.
Sustainability in the Development of the Urban Eco-environment
Authors: Tonev Mladen
Published: May 2021

The article considers the main parameters of the sustainable development of the urban environment as a basis for ecological development of the major Bulgarian Black Sea cities - Varna and Burgas. Based on the problems of urbanization in the post-totalitarian transition in Bulgaria, conclusions and findings are made about the nature and characteristics of the formed urban communities in the leading port cities of the Republic of Bulgaria in the Black Sea. The thesis is defended that the future development of our Black Sea cities should be based on environmental friendliness and sustainability. They should strive for a coastal fluidity, with a transition from one urban environment to another, with a panorama of a cultural collage that combines aspects of the ecological urban environment and architecture with the challenges of technology and modern transport and communication infrastructure. An attempt has been made to highlight the positive and negative changes in the development of the Black Sea cities over the last three decades. The main guidelines for the necessary changes in the regulatory aspect are presented. They should ensure the protection of the air, soil, water and nature of the Black Sea region.
An Assessment on Performances of Public and Private Waste Management Systems in Sri Lankan Cities
Authors: Hettiarachchi Udeshika , Kariyawasam Shanaka , Senevirathne Chameli
Published: May 2021

Sri Lanka, being a developing country, currently undergoes high influx of population, rapid infrastructure developments and increasing urbanization. These have paved the way for the increase of solid waste generation rates in the country. However, the majority of the Sri Lankan cities have failed to manage their waste sustainably due to lack of proper management system. Assessment of the existing solid waste management system would be an important step towards developing a sustainable SWMS in the future for these cities. In this context, this study aims to investigate the performances of public and private sector waste management systems, to learn from each sector by identifying the positive and negative aspects of their performances and to identify the ways that can uplift the entire solid waste management system sustainably. The study employed both qualitative and quantitative data collection methods in the Negombo municipal council area whereas Multi-criteria analysis was incorporated as the main analysis technique. Findings revealed that, Private sector has better performance in economic and social measures than the Public sector whereas the Public sector has better performance in environmental measures. Accordingly, findings suggest that public private partnerships, performance measuring, regulating and benefit and risk sharing mechanisms should be incorporated towards the long-term sustainability of future SWMS.
Strategies of investigating and translating poetical prose of the classical and contemporary English short stories
Authors: Yemets Alexander , Zakharchuk Anastasiia
Published: May 2021

The article considers the notion of prose poeticalness from linguistic and translation points of view. Prose poeticalness can be defined as the introduction of poetic features into the prose text with the help of such devices as extended metaphors, intertextual allusions, stylistic convergence, syntactical and phonetic repetitions. The investigation involved the analysis of the fairy tales by Oscar Wilde, the short stories by Kate Chopin and Dylan Thomas, which are referred to as classical prose, and the contemporary American flash fiction stories. The strategy of investigating prose poeticalness involved determining the devices of prose poeticalness in each text, defining the linguistic and stylistic components of these devices and their functions. As a result of our research, it is determined that the most foregrounded device of poeticalness is stylistic convergence. In the classical short stories, convergences function in bigger text fragments, they are based on the extended antropomorphic metaphors or similes in the interaction with alliterations. The stylistic convergences are used for poetical description of nature as human beings possessing the ability to speak, to think, to love (Wilde, Thomas), and even as gods (Rob Carney). Biomorphic tropes are used as the core of convergences, as a device of poetical description of people in the stories by Thomas, fairy tales by Wilde, in the flash fiction stories by John Updike, Grace Paley, Leigh Wilson and other writers. In the contemporary flash fiction stories, convergences foreground the ideas of sympathy, tolerance; they help to create a strong emotional effect. The strategy of rendering stylistic convergences in translation of the poetical prose consists in the exact reproduction of images applying literal translation or synonymic substitution and retaining the sound effect in trope components. Mythological and biblical allusions used as a system in the text are a device of poeticalness typical for Thomas's stories. The strategy of translating implicit allusions involves retaining the intertextual comments and giving explication in the text or in the footnotes. It is suggested that the prospects of further research lie in investigating poeticalness in the novels of contemporary writers.
H2O2-Promoted Alkylation of Quinoxalin-2(1H)-ones with Styrenes and Dimethyl Sulfoxide
Authors: Yao Hua , Lin Sen , Zhong Xiaoyang , Wang Bingqing , Yan Zhaohua , Xiong Feng
Published: May 2021

A hydrogen peroxide (H2O2)-mediated quinoxaline-2(1H)-ones hydrocarbylation reaction has been reported. The reaction is achieved through the difunctionalization of styrene. In this transformation, methyl radical resulting from dimethyl sulfoxide firstly attacks styrenes to provide alkyl radicals which then undergo alkylation at the C3 position of quinoxalin-2(1H)-one. A green, convenient, and simple protocol for the synthesis of 3-alkylquinoxalin-2(1H)-ones was provided.
Homeopathic Treatment in Patients with Polycystic Ovarian Syndrome: A Case Series
Authors: Parveen Suraia , Das Subhrasankha
Published: May 2021

Background and Objectives Polycystic ovary syndrome (PCOS) is a common heterogeneous endocrine disorder in women of reproductive age. It is characterized by various clinical presentations such as ovulatory dysfunction, polycystic ovaries, and hyperandrogenism. Considering the side effects associated with conventional treatment and the patients who fail to respond to these measures, there is a demand for a complementary therapy that would alleviate symptoms of PCOS without side effects. Homeopathy is a complementary system of medicine that has been successfully used in different disease conditions, including PCOS. A case series of PCOS is hereby presented, to demonstrate some positive results of individualized homeopathic treatment.

Methods Seven cases of young women with PCOS were treated with individualized homeopathic medicines. Each case was followed up with clinical and ultrasonographic evidence and was reported according to the criteria set out in the HOM-CASE guidelines. The assessment of causal attribution of homeopathic treatment effect was carried out using the Modified Naranjo Criteria.

Results Marked improvement was observed in all seven cases of PCOS. The irregular menstrual cycles and other associated symptoms became normal, along with a resolution of cysts in ovaries as evidenced by ultrasonography. All cases improved within 4 to 12 months of treatment. The Modified Naranjo Criteria total score was +9/13 for each case, which indicates a positive causal attribution of homeopathy in relieving the symptoms of PCOS.

Conclusion This case series suggests a significant role of individualized homeopathic medicines in PCOS by regularizing the menstrual cycle along with the resolution of cysts and associated symptoms.
Influence of the Head Neck Position on Imaging Measurements Used to Assess the Craniovertebral Junction in Small Breed Dogs: A Cadaveric Study
Authors: Planchamp Bastien , Forterre Franck , Vidondo Beatriz , Beugger Angela , Müller Andrea , Precht Christina
Published: May 2021

Objective The study aimed to determine the influence of head neck position on imaging measurements used to assess the craniovertebral junction (CVJ) and to recommend the most appropriate position for the evaluation of the CVJ.

Study Design A cross-sectional sample of adult dogs' cadavers was subjected to a computed tomography scan of the cranium and the cranial cervical region in three standardized head positions. Imaging measurements often used to assess the CVJ were measured. The influence of the head neck position, breed, weight and gender on imaging measurements was tested using repeated measures analysis of variance.

Results Twenty-eight cadavers of small breed dogs were enrolled in the study. All cadavers examined had occipital dysplasia. All transarticular imaging measurements were dependent on the head neck position. In addition, the breed, weight and gender had an influence on several measurements.

Conclusion We recommend a standardized head neck position of 50 degrees flexion if quantitative imaging measurements of the CVJ are used to diagnose pathologies in this region. Future studies should focus on the definition of cut-off values for quantitative imaging measurements of the CVJ to differentiate between healthy and diseased small breed dogs. Regarding atlantoaxial instability, a combination of six parameters (C1-C2 angle, C1-C2 overlap, atlantoaxial distance, dens-to-axis length ratio, ventral compression index and clivus canal angle) is promising for its diagnosis.
Proposing an International Standard Accident Number for Interconnecting Information and Communication Technology Systems of the Rescue Chain
Authors: Spicher Nicolai , Barakat Ramon , Wang Ju , Haghi Mostafa , Jagieniak Justin , Öktem Gamze Söylev , Hackel Siegfried , Deserno Thomas Martin
Published: May 2021

Background The rapid dissemination of smart devices within the internet of things (IoT) is developing toward automatic emergency alerts which are transmitted from machine to machine without human interaction. However, apart from individual projects concentrating on single types of accidents, there is no general methodology of connecting the standalone information and communication technology (ICT) systems involved in an accident: systems for alerting (e.g., smart home/car/wearable), systems in the responding stage (e.g., ambulance), and in the curing stage (e.g., hospital).

Objectives We define the International Standard Accident Number (ISAN) as a unique token for interconnecting these ICT systems and to provide embedded data describing the circumstances of an accident (time, position, and identifier of the alerting system).

Materials and Methods Based on the characteristics of processes and ICT systems in emergency care, we derive technological, syntactic, and semantic requirements for the ISAN, and we analyze existing standards to be incorporated in the ISAN specification.

Results We choose a set of formats for describing the embedded data and give rules for their combination to generate an ISAN. It is a compact alphanumeric representation that is generated easily by the alerting system. We demonstrate generation, conversion, analysis, and visualization via representational state transfer (REST) services. Although ISAN targets machine-to-machine communication, we give examples of graphical user interfaces.

Conclusion Created either locally by the alerting IoT system or remotely using our RESTful service, the ISAN is a simple and flexible token that enables technological, syntactic, and semantic interoperability between all ICT systems in emergency care.
A Scary Complication: Single-center Study on Management and Outcome of Cesarean Scar Pregnancy
Authors: Hüner Beate , Lato Krisztian , Reister Frank , Janni Wolfgang , Deniz Miriam
Published: May 2021

A cesarean scar pregnancy (CSP) is a scary and life-threatening complication of cesarean section (CS). Nevertheless, the incidence of CS is constantly growing. The CSP incidence is 0,15% of pregnancies after CS which represents 6,1% of all ectopic pregnancies in women with condition after CS. Therefore, it should be more present in the clinical daily routine. From mild nonspecific symptoms to hypovolemic shock, diagnosis and therapy must be performed quickly. With the progressive growth of the scar pregnancy, a uterine rupture involves the risk of severe bleeding, and an emergency hysterectomy could be necessary. Prolongation of pregnancy has been successful only in a few cases. We report 11 cases from our hospital in the past 10 years. In the discussion, treatment options of this complication with an increasing incidence, which is associated with serious morbidity and mortality, are presented based on the current literature. Treatment options include drug therapy, but also surgical or combined procedures with radiological intervention.
The effects of suprathermal particles on the existence domain of oblique low-frequency solitary waves in multi-component magnetospheric plasmas
Authors: Rufai O. R. , Bharuthram R. , Maharaj S. K.
Published: May 2021

The effect of suprathermal particles is examined on arbitrary amplitude nonlinear low-frequency electrostatic solitary waves propagating obliquely to the ambient magnetic field of the terrestrial magnetosphere using the Sagdeev pseudopotential formalism. The four-component plasma model consists of cold singly charged oxygen ions, hot protons, and two distinct groups of electrons with the latter three having kappa velocity distributions. Our numerical investigations based on comparatively low values for the spectral indices of the two electron species and the hot proton distributions as inferred from time history of events and macroscale interactions during substorms mission data reveal that the coexistence of compressive and rarefactive solitons is suppressed in comparison to the behavior in the presence of Maxwellian species (infinitely large values of kappa). Also, the existence of positive potential solitons is suppressed in an intermediate range of cold oxygen-ion densities. The differences are attributed to the occurrence of singularities in the Sagdeev potential for the chosen set of spectral indices.
Solutions to linear dissipative quantum systems
Authors: López P. C. , Santos-Silva R. , García A.
Published: May 2021

We use the characteristic function of the Wigner function (its double Fourier transform) to give solution to any generic open quantum linear systems (systems whose Hamiltonian is at most quadratic). The solution is carried out in terms of the application of the transition matrix of the dynamical evolution in the Fourier space. We address two cases: the time-independent coefficients for which we give the solutions for several dissipative models of the quantum harmonic oscillator and the one-dimensional free particle. In the latter, we also derive a heuristic model for a pure damped motion with suppression of diffusion. For the time-dependent coefficient problem, we give some particular cases that are integrable and derive a second order approximation to the generic case in which all parameters are time-dependent. We additionally explore the solutions of the system when the diffusion processes of the dissipative model lie beyond the weak coupling limit.
Au11Ag6 nanocluster: Controllable preparation, structural determination, and optical property investigation
Authors: Zhou Chuanjun , Li Hao , Ke Feng , Zhu Chen , Pan Peiyao , Xu Wen Wu , Kang Xi , Song Yongbo , Zhu Manzhou
Published: May 2021

The structure/composition of nanoclusters has a decisive influence on their physicochemical properties. In this work, we obtained two different Au–Ag nanoclusters, [Au9Ag12(SAdm)4(dppm)6Cl6]3+ and Au11Ag6(dppm)4(SAdm)4(CN)4, via controlling the Au/Ag molar ratios by a one-pot synthetic approach. The structure of nanoclusters was confirmed and testified by single-crystal x-ray diffraction, electrospray ionization time-of-flight mass spectrometry, XPS, powder x-ray diffraction, and electron paramagnetic resonance. The Au11Ag6 nanocluster possessed a M13 core caped by four Au atoms and four dppm and four AdmS ligands. Interestingly, four CN are observed to locate at the equator of the M13 core. Both nanoclusters contain a similar icosahedral M13 core, whereas their surface structures are totally different. However, the Au11Ag6 nanocluster exhibits good stability and strong red photoluminescence in solution.
Ultra wide-angle and broad-band metamaterial absorber based on magneto-electric dipole structure
Authors: Wang Aixia , Qu Shaobo , Wang Jiafu , Zhang Jieqiu , Wang Wenjie , Xu Cuilian
Published: May 2021

An ultra wide-angle and broad-band magneto-electric dipole like metamaterial absorber (MEDMA) was proposed. The trapezoidal resistance films on the top layer and the upright resistance films in the middle are both equivalent to electric dipoles. The metal back plate together with the resistance films on the top layer are equivalent to magnetic dipoles. The radiation characteristics of magnetic dipole and electric dipole determine that the composite structure can achieve low back radiation effect and equal E-plane and H-plane patterns. According to reciprocity principle, the composite structure will also have a better absorption performance when it is used as an absorber. Simulation results show that the absorption of the MEDMA is more than 90% under TM polarized waves of 3.4–8.0 GHz as the incident angle changes from 0° to 80°. For TE polarized waves of 3.2–9.0 GHz, the absorption with the incident angles of 0°–50° is more than 80%. The absorption performance for each part of the MEDMA was analyzed by the surface current distributions, and the impedance matching characteristics was demonstrated by Smith chart. This work may provide a technical way in stealth research.
Stability of the planar rarefaction wave to three-dimensional Navier–Stokes–Korteweg equations of compressible fluids
Authors: Li Yeping , Luo Zhen
Published: May 2021

This study is concerned with the large time behaviour of the three-dimensional isentropic compressible Navier–Stokes–Korteweg equations, which are used to model viscous and compressible fluids with internal capillarity. Based on the fact that the rarefaction wave is nonlinearly stable to the one-dimensional isentropic compressible Navier–Stokes–Korteweg equations, the planar rarefaction wave to the three-dimensional isentropic compressible Navier–Stokes–Korteweg equations is first constructed. Then it is shown that the planar rarefaction wave is asymptotically stable in the case that the initial data are a suitably small perturbation of the planar rarefaction wave and the strength of the rarefaction wave is small. The proof is based on the delicate energy method. The result indicate that the planar rarefaction wave of the inviscid Euler system is stable for the three-dimensional isentropic compressible fluids with physical viscosities and internal capillarity.
Periodic travelling waves on damped 2D lattices with oscillating external forces
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Authors: Zhang Ling , Guo Shangjiang
Published: May 2021

This paper is devoted to periodic travelling waves in a two-dimensional nonautonomous weakly damped lattice system with linear coupling between nearest particles and periodic nonlinear substrate potentials. Nonlinear functional analysis is employed to prove the existence and uniqueness of periodic travelling wave solutions. In the case of small forcing and damping, Lyapunov–Schmidt reduction is employed to study the bifurcation of periodic travelling wave solutions and the asymptotic expressions of the bifurcating solutions.
Vibration isolation concept by switchable stiffness on a semi-active pneumatic actuator
Authors: Mikułowski Grzegorz
Published: May 2021

In this paper a novel technique of switchable stiffness dedicated to vibration isolation is presented. The approach utilises a semi-active pneumatic device in which the stiffness switching is obtained via controlled thermodynamic processes. The concept for the dissipation technique is introduced and a mathematical model is proposed. The system is analysed under passive and semi-active modes of operation by means of numerical simulation and in an experimental survey. The analysis consists of the model validation, an energy dissipation process study and a verification of effectiveness of the concept under varying operational conditions. As a result, it is demonstrated that the proposed technique allows for combining advantages of controllable pneumatic springs and pneumatic dampers, which constitutes an added value. It is revealed in the conducted tests that the system allows for 147% increase in energy dissipation per vibration cycle and reduce the resonant amplitude peak by 8%, both in comparison to a passive gas damper. The presented concept introduces an innovative approach to the switching stiffness techniques dedicated to vibration mitigation. The findings may significantly expand the number of their implementation possibilities.
Out-of-plane wave propagation in two-dimensional micro-lattices
Authors: Sepehri Soroush , Mosavi Mashhadi Mahmoud , Seyyed Fakhrabadi Mir Masoud
Published: May 2021

Unlike the extensive studies on the in-plane motion of macroscale lattices, their out-of-plane motion has received drastically less attention in the mechanical engineering community. However, the practical limitations of the detection of very high-frequency in-plane vibrations in small-scale structures have restricted their investigations considerably leading the researchers toward their out-of-plane analysis. The necessity of measuring the out-of-plane displacements of the periodic lattices, especially in small-scale structures, demands a thorough perception of their out-of-plane behavior. As a result, in this paper, the size-dependent out-of-plane wave propagation of periodic micro-lattices with hexagonal, square, triangular, and kagome topologies is investigated using the finite element method and Bloch’s theorem. To include size-dependency, the modified couple stress theory is used and the governing equations of the flexural and torsional motion of the small-scale microbeams are obtained. Furthermore, for the analysis of the out-of-plane wave propagation, the unit cells are discretized into grid elements, with three degrees of freedom (out-of-plane displacement, torsion, and out-of-plane bending) at each node. Also, the directionality of the out-of-plane waves at low frequencies is investigated by analyzing the iso-frequency contours of each structure. The results reveal that the size-dependency has a major contribution in determining the propagation, attenuation, and directionality of waves in small-scale micro-lattices. However, As the dimension of the structure becomes larger, the impact of size-dependency fades away and the behavior of small-scale structures becomes closer to that of classical structures.
CMB lensing power spectrum estimation without instrument noise bias
Authors: Madhavacheril Mathew S. , Smith Kendrick M. , Sherwin Blake D. , Naess Sigurd
Published: May 2021

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

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.
Unusual electronic structure of Dirac material BaMnSb2 revealed by angle-resolved photoemission spectroscopy*
Authors: Rong Hongtao , Zhou Liqin , He Junbao , Song Chunyao , Xu Yu , Cai Yongqing , Li Cong , Wang Qingyan , Zhao Lin , Liu Guodong , Xu Zuyan , Chen Genfu , Weng Hongming , Zhou Xingjiang
Published: May 2021

High resolution angle resolved photoemission measurements and band structure calculations are carried out to study the electronic structure of BaMnSb2. All the observed bands are nearly linear that extend to a wide energy range. The measured Fermi surface mainly consists of one hole pocket around Γ and a strong spot at Y which are formed from the crossing points of the linear bands. The measured electronic structure of BaMnSb2 is unusual and deviates strongly from the band structure calculations. These results will stimulate further efforts to theoretically understand the electronic structure of BaMnSb2 and search for novel properties in this Dirac material.
Realization of semiconducting Cu2Se by direct selenization of Cu(111)*
Authors: Yang Yumu , Wu Qilong , Deng Jiaqi , Wang Jing , Xia Yu , Fu Xiaoshuai , Tian Qiwei , Zhang Li , Yin Long-Jing , Tian Yuan , Xie Sheng-Yi , Zhang Lijie , Qin Zhihui
Published: May 2021

Bulk group IB transition-metal chalcogenides have been widely explored due to their applications in thermoelectrics. However, a layered two-dimensional form of these materials has been rarely reported. Here, we realize semiconducting Cu2Se by direct selenization of Cu(111). Scanning tunneling microcopy measurements combined with first-principles calculations allow us to determine the structural and electronic properties of the obtained structure. X-ray photoelectron spectroscopy data reveal chemical composition of the sample, which is Cu2Se. The observed moiré pattern indicates a lattice mismatch between Cu2Se and the underlying Cu(111)-

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surface. Differential conductivity obtained by scanning tunneling spectroscopy demonstrates that the synthesized Cu2Se exhibits a band gap of 0.78 eV. Furthermore, the calculated density of states and band structure demonstrate that the isolated Cu2Se is a semiconductor with an indirect band gap of ∼ 0.8 eV, which agrees quite well with the experimental results. Our study provides a simple pathway varying toward the synthesis of novel layered 2D transition chalcogenides materials.
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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.