bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulator development of a rotary magnetocaloric refrigerator by stepwise regenerator modelling approach
Authors: Câmara L D T , Tedesco J C G 
Published: February 2021

Abstract
Magnetic refrigeration has been seeing as a promising technology based on the magnetocaloric effect. One of its great advantages is it offers smaller global environmental impact relating to conventional refrigeration. Modeling and simulation of such processes can provide important data in the development and optimization of the experimental devices. Among existing designs, the rotary refrigerators presents several challenges in terms of complexity when comparing to reciprocating ones, which is compensated by several properties. A novel full process simulator of a magnetocaloric refrigerator processes was implemented to study the processes performance over different conditions. A stepwise modeling approach was applied, simplifying the phenomena of heat transfers. Gd was chosen as refrigerant material because of its magnetic transition temperature. The routine considered a rotating clockwise Gd wheel with an anticlockwise closed flow loop of water, which percolates the six Gd porous beds, hot and cold heat exchanger. The simulator was able to represent the transient aspects as well as the steady state conditions of the processes, considering both time performance and numerical stability. The inversion in heat transfer profiles along the process was used as a limit in the calculation of the maximum heat transfer absorption in the cold exchanger.
On dark stars, galactic rotation curves and fast radio bursts
Authors: Nikitin Igor 
Published: February 2021

Abstract
This paper is a continuation of our recent work on Radial Dark Matter stars (RDM-stars), black holes, coupled with radial flows of dark matter. As a galaxy model, it produces flat rotation curves, approximately valid for many galaxies far from the center. In this paper, more detailed modeling is carried out, including the vicinity of the galactic center. Assuming that the distribution of stellar black holes repeats the distribution of luminous matter, we get a perfect match between the model rotation curves and the observed ones. Further, using numerical integration, we examine the gravitational field of an individual RDM-star. The computation shows the event horizon being erased and rapidly increasing mass density arising instead (mass inflation). In this regime, we apply the previously constructed Planck star model, where at high densities a repulsive force occurs (quantum bounce). In our stationary model, the evolution of a Planck star has stopped under the pressure of dark matter flows. This system is considered as a possible source of Fast Radio Bursts (FRBs). In a scenario involving an asteroid falling onto an RDM-star, the model reproduces the correct frequency range of FRBs. Their total energy, coherence and short duration are explained as well.
Mathematical modeling and visualization of topologically non-trivial solutions in general relativity
Authors: Nikitin Igor 
Published: February 2021

Abstract
In general relativity, there is a class of solutions that currently do not have observed analogues, but on which the theory is shaped, giving an understanding what is fundamentally possible within its framework. Such solutions include wormholes, tunnels that connect distant regions in spacetime. Although not a single wormhole has yet been discovered, there is a large number of works devoted to their study, thanks to which wormholes as a class of solutions become firmly established in modern science. In this paper, we consider two topologically nontrivial types of solutions related to wormholes. First: wormholes that can open and close. In this relation, we will discuss topological censorship theorems, which under certain conditions prohibit changing topology. We will also discuss known ways to circumvent these theorems. Using analytical and numerical methods, as well as visualization, we will construct an example of an opening and closing wormhole with the dimensions of the central black hole in the Milky Way galaxy. Our construction continues the work by Kardashev, Novikov and Shatskiy, in which a static wormhole with the same parameters was considered. The second type is a modification of Visser’s dihedral wormhole solution for a dynamic case.
Using Particle Swarm Optimization for design comb compensator with magnitude response synthetized as sine function
Authors: Salguero Luna S , Jovanovic Dolecek G , Fernández De Lara Sosa A 
Published: February 2021

Abstract
Comb compensator improves the passband characteristic of comb filter, i.e. decreases the comb passband droop. This paper presents one method for a comb compensator design with the magnitude response synthetized as sine function. The parameter of design is the amplitude of sine function denoted as A. The goal is to find the amplitude of sine function A for each value of comb parameter, K, K=1, …,5, where K is the number of the cascaded comb filters. First the optimum values of the amplitude of sinusoidal function A, for each value of K, K=1, …,5 are obtained using Particle Swarm Optimization (PSO). It is demonstrated that the obtained values A practically do not depend on the decimation factor M, for M>10. In next step the obtained values of the parameter A are presented as sum of powers of two (SPT) to get a multiplierless design. The method is illustrated with one example and compared with the methods from literature.
Deliberative architecture for smart sensors in the filtering operation of a water purification plant
Authors: Mendoza E. , Andramuño J. , Núñez J. , Benítez I. 
Published: February 2021

Abstract
The increase of applications for industrial smart sensors is booming, mainly due to the use of distributed automation architectures, industrial evolution and recent technological advances, which guide the industry to a greater degree of automation, integration and globalization. In this research work, an architecture for deliberative-type intelligent industrial sensors is proposed, based on the BDI (Belief Desire Intentions) model, adaptable to the measurement of different variables of the filtering process of a water purification plant. An intelligent sensor with functions of signal digitalization, self-calibration, alarm generation, communication with PLC, user interface for parameter adjustment, and analysis with data extrapolation have been arranged. For decision making, the use of fuzzy logic techniques has been considered, which allows imprecise parameters to be appropriately represented, simplifying decision problem solving in the industrial environment, generating stable and fast systems with low processing requirements. The proposed architecture has been modelled, simulated and validated using UML language in conjunction with Petri nets, which facilitate the representation of discrete system events, presenting them clearly and precisely. In the implementation and testing of the prototype, C/C ++ language has been used in an 8-bit microcontroller, experimentally corroborating the operation of the device, which allowed evaluating the behavior of a pseudo-intelligent agent based on the requirements of the water treatment plant, and also through comparisons with similar works developed by other researchers.
Topological climate change with permafrost feedback
Authors: Kypke Kolja L , Langford William F , Nethercott Nathaniel , Willms Allan R 
Published: February 2021

Abstract
Climate models predict that the climate of the Earth is warming and will continue to warm in coming centuries, if there is no mitigation. A recent energy balance model [Kypke et al., Nonlin. Process. Geophys.
27 (2020) 391–409] forecasts that, if the current increase of carbon dioxide in the atmosphere continues unabated, then in the next century the climate of the Earth will not only get warmer, but will transition abruptly via a bifurcation, to a warm equable climate unlike any climate seen on Earth since the Pliocene. This transition to a new climate state is a topological change. That model includes the effects of water vapour feedback and ice albedo feedback, as well as ocean and atmospheric heat transport. This paper adds to that model further amplification by permafrost feedback. That is, as the Arctic warms, permafrost will thaw, releasing large amounts of the greenhouse gases carbon dioxide and methane, which cause further warming. Since knowledge of permafrost stores and release rates is limited, a range of permafrost carbon release sensitivities (Q
10) is considered. The model predicts that permafrost feedback accelerates the timing and increases the likelihood of a topological climate change in the Arctic, and reinforces the view that permafrost feedback should not be ignored in Anthropocene climate models.
The influence of the load’s geometrical characteristics on the generation of the electro-thermo-mechanical instability in a single wire Z-pinch
Authors: Kaselouris E , Tamiolakis G , Dimitriou V , Tatarakis M 
Published: February 2021

Abstract
The Z-pinch plasma device is a type of plasma confinement system that uses electrical current to generate a magnetic field which compresses a current-carrying wire. In a previous proof-of-principle study, we demonstrated that in the interaction of a single wire with a pulsed current, the generated Electro-Thermo-Mechanical (ETM) instability in the solid phase acts as a seeding mechanism for the later developed instabilities observed in the plasma phase. In this study, the influence of the geometrical characteristics, such as length and thickness of the load-wire, on the generation of the ETM instability are investigated. Finite element multiphysics-multiphase simulations starting from the solid state are coupled with Magneto-Hydro-Dynamics (MHD) simulations to study the solid to plasma phase transition and the matter’s dynamics. The numerical results of the wire expansion dynamics prior to plasma formation are validated by experimental results from a modified Fraunhofer diffraction diagnostic, while in the plasma phase the simulated plasma dynamics is validated by shadowgraphic and interferometric experimental results. The numerical and experimental results demonstrate a satisfactory agreement for the wire expansion dynamics and the growth rate of the developed instabilities, for varying wire thickness and length.
Predicting the Behaviour of a Vortex Shedding-Based Passive Mechanical Micro Heat Exchanger
Authors: Granados-Ortiz F-J , Garcia-Cardosa M , Ortega-Casanova J 
Published: February 2021

Abstract
In the recent years, microscale applications are gaining increasing importance. Despite their advances, the technology and resources needed to develop new designs may be a drawback for reduced scale engineering testing. To overcome this, computational methods are an efficient tool to predict how a real-life system may behave prior physical construction. The present work aims to investigate numerically effective models to predict the conditions at which a micro heat exchanger (MHE) is able to promote mixing by vortex shedding mechanics. In spite of vortex-shedding is a well-known mechanism in flow physics, it is not possible to know a priori whether a configuration (for a given geometry and flow velocity) may or may not lead to this desired vortex detachment to enhace mixing. Thus, Machine Learning methods are used for prediction, trained with finite-volume numerical simulations of different MHE devices selected based on their performance. A classification model is used to predict which configurations lead to vortex shedding. Also, a correlation regression model is developed to predict the critical Reynolds number. When the critical Reynolds number is surpassed for a given geometry, vortex shedding appears and its intensity controls the thermal mixing efficiency of the microdevice. These predictors could be useful in the search of optimal configurations by optimisation algorithms, since in the sampling process could be used to define constrains.
Simulation of Time-Lapse Resistivity Logging During Two-Phase Well Testing in Petroleum Reservoirs
Authors: Shishkina O A , Indrupskiy I M , Kovalenko K V , Makarova A A , Zakirov E S , Anikeev D P , Anikeeva E S 
Published: February 2021

Abstract
Well testing methods are widely used in petroleum industry to identify reservoir parameters in-situ, at real reservoir flow conditions. Two-phase tests with water injection extend capabilities of well testing to evaluation of oil-water flow characteristics through the solution of an inverse problem based on well measurements during the test. Near-wellbore water saturation is used as one of the informative measured parameters. However, water saturation is actually not directly measured on wells. Instead, it is interpreted from time-lapse well logging data, with resistivity logging being one of the options. This means that forward and inverse problems are to be extended to incorporate direct simulations of resistivity logging. In this paper we address the forward problem. It is formulated and solved for different types of logging tools, both for open hole and through the casing. A numerical algorithm and software implementation have been developed for repeated solution of an axisymmetric forward problem of resistivity logging – a 2D elliptical partial differential equation for electrical potential. Distributions of formation resistivity at the moments of logging are calculated from distributions of water saturation and salinity. The latter are computed through numerical solution of the forward problem of well testing – a two-phase oil-water flow in the reservoir with changing salinity of the water phase, with full account for real fluid and reservoir properties. The software implementation of the resistivity logging problem has been tested in comparison with the known theoretical solutions. Examples are presented to show how time-lapse changes in resistivity logging data reflect the specifics of the two-phase flow with changing water salinity during the well test.
Design of miniature directional coupler with wide bandwidth
Authors: Letavin Denis A , Alaev Danil P 
Published: February 2021

Abstract
Miniature directional coupler with wide bandwidth consisting of compact structures and curved lines has been developed. The type of structures was chosen in such a way as to achieve the greatest possible coincidence of their characteristics in the bandwidth with the characteristics of quarter-wave sections. The area of the developed coupler is 69.8% less than the area of the same device in its standard version. Device modeling was performed in the Cadence AWR program. It is shown that miniaturization of the directional coupler caused deterioration of such characteristics as operating frequencies band, preservation of the phase differences between the outputs in a wide frequencies band, and attenuation in the band. A model of the coupler was made, which allowed us to confirm experimentally the correctness of calculations in AWR.
A compact 3-dB coupler with microstrip cells
Authors: Letavin Denis A , Alaev Danil P 
Published: February 2021

Abstract
Research of the design of a coupler with an operating frequency of 1.8 GHz has been conducted. This construction has a small area and can be used in microwave circuits for power division. Suggested construction, taking into consideration the reduced dimensions, has characteristics comparable to the design in the traditional version. Miniaturization of the device was achieved by using synthesized microstrip cells which were installed instead of ordinary sections. The coupler was modeled and fabricated and the measured characteristics are well coincide with the calculations.
Sharing economy as a part of the sustainable development concept
Authors: Absalyamov T , Absalyamova S , Mukhametgalieva Ch , Sakhapov R 
Published: February 2021

Abstract
The article is devoted to the study of sharing economy as a new economic model. Today, sharing economy or economy of joint consumption, is in serious competition with traditional industries. The paper presents basic approaches to determination of the sharing economy essence. It considers the factors contributing to its formation and growth. Among the main factors, the authors highlight technological, economic, environmental and social factors. The paper studies the development dynamics of individual sectors of the joint consumption economy in Russia, their contribution to the implementation of the Sustainable Development Goals. Moreover, the authors explore new trends, such as the expansion of geography, changes in the demographic composition of participants, and the integration of sharing in ecosystems. The risks of further expansion of the sharing economy are studied as well - the risk of personal data leakage, problems with the state of critical infrastructure etc.
A comparison of numerical solvers for the delay eigenvalue problem of coupled oscillators
Authors: Abdelrahman Abdelrahman S. , Al-Qahtani Hussain , Alharbi Fahhad H. 
Published: February 2021

Abstract
In this work, we conduct a comparison for various delay differential equations’ solvers to determine the strength and weakness points of each one. The comparison is clarified through a numerical example in which we consider the coupled harmonic oscillators. We obtain the eigenvalues of the delayed coupled harmonic oscillators system by solving the governing equations by all considered methods. However, the methods of concern in this paper are as follows: the Taylor series expansion, Rekasius’s substitution, self-consistent approach, and the Krylov method with Chebyshev interpolation. The main aspects that we investigate in this paper are the stability, robustness, and numerical efficiency. We found that the Krylov method with Chebyshev interpolation performs better than all the other considered ones.
A mathematical model for calculation of the influence of ferromagnetic components in Vertical Displacement Events and stability simulations of tokamak plasmas
Authors: Atanasiu Calin V. , Zakharov Leonid E. , Hoelzl Matthias , Gerasimov Sergei 
Published: February 2021

Abstract
Iron core transformer tokamaks have a distinct element, namely the iron core which can affect the plasma stability of the plasma. As a consequence of the high non-linear dependence of the magneto-hydrodynamic solutions on the iron permeability μ

Fe
in JET tokamak for example, Vertical Displacement Events (VDEs), equilibrium and stability calculations are more complicated and more time consuming than in air core transformer tokamaks. By considering the ferromagnetic components as a linear, isotropic and homogeneous media on subdomains, it is known that these media can be replaced by a homogeneous one (vacuum) and a surface-current density distribution i

Fe(l) on the separation surfaces between subdomains, with l the curve taken along the curve separating two different magnetic media. For the case of geometry with rotational symmetry, this surface-current density distribution along a curve, in a meridian plane, is given by a Fredholm integral equation of second kind. Practically, the advantage of this method is more obvious for the inverse formulation of the VDEs and stability problems by moving the non-linear term (due to the iron permeability μ

Fe
) from the differential operator to the r.h.s. of the equations. In this paper, we are presenting how the influence of ferromagnetic components in the equations of the surface currents developed in the vessel structures during Wall Touching Kink Modes (WTKMs) can be taken into account and are reviewing the equations to be solved in order to simulate the influence of the ferromagnetic components in VDEs and equilibrium stability calculations. The numerical results of these simulations for a real JET tokamak structure and plasma parameters will be reported in a future paper.
Problems of attracting foreign direct investment into the regional economy
Authors: MGaleeva G , Kadeeva E N 
Published: February 2021

Abstract
The article discusses topical issues of attracting foreign direct investment in the economy of the Republic of Tatarstan. The assessment of the factors affecting the investment attractiveness of Russian regions made it possible to determine the prospects for the implementation of projects with the participation of foreign investors. In conclusion, the authors highlight the successful practices of attracting foreign investment in the region’s economy.
Differential operators and the symmetric groups
Authors: Nonkané Ibrahim 
Published: February 2021

Abstract
In this paper, we study the action of the rational quantum Calogero-Moser system on polynomials. In this vein, we study polynomials ring over the complex field ℂ as a module over a ring of differential operators by elaborating its irreducible submodules. we endowed the polynomial ring ℂ[x
1
, …, x

n
] with a differential structure by using directly the action of the Weyl algebra associated with the ring of symmetric polynomial ℂ[x
1
, …, x

n
]
Sn after a localization. Then we study the polynomials representation of the ring of invariant differential operators under the symmetric group. We use the representation theory of symmetric groups to exhibit the generators of its simple components.
Analysis and modeling of Fano resonances in coupled cantilevers
Authors: Baquero Hugo Aya 
Published: February 2021

Abstract
The coupled oscillators model has been used for decades to interpret the Fano interference in a variety of systems: optical, plasmonic, and microwave. Hence, Fano resonance can be modeled with a weak or tightly coupled mechanical oscillators system, which provide insight into the interaction dynamics of a radioactive continuum of propagation modes and a discrete state. Therefore, the coupled cantilevers model was implemented in a FEM routine, in order to study and discuss aspects of the Fano resonance. The study of the Fano resonance in coupled cantilevers shows that this model may be applied in the field of micromechanical sensors.
High energy neutrino and gamma-ray emissions from the jets of M33 X-7 microquasar
Authors: Papadopoulos D A , Papavasileiou Th V , Kosmas T S 
Published: February 2021

Abstract
In this work, after testing the reliability of our algorithms through numerical simulations on the well-studied SS 433 Galactic microquasar, we focus on neutrino and γ-ray emissions from the extragalactic M33 X-7 system. This is a recently discovered X-ray binary system located in the neighbouring galaxy Messier 33 which has not yet been modelled in detail. The neutrino and γ-ray energy spectra, produced from the magnetized astrophysical jet of M33 X-7, in the context of our method are assumed to originate from the decay (and scattering) processes taking place among the secondary particles produced assuming that, first, hot (relativistic) protons of the jet scatter on thermal ones (p-p interaction mechanism).
Exploiting Dirac equations solution for exact integral calculations in processes of muonic atoms
Authors: Giannaka P.G. , Kosmas O. , Tsoulos I. , Kosmas T.S. 
Published: February 2021

Abstract
Precise muon wave functions are calculated by solving the Dirac equations within a method based on modern neural networks and stochastic optimization techniques. The reduced radial wave functions (up and bottom) of a bound muon in muonic atoms are then given as linear combinations of the well behaved sigmoid functions. As concrete applications, the known muonnucleus overlap integrals, which determine the structure and evolution of muonic atoms (twobody quantum systems bound together due to the fundamental electromagnetic interactions), may accurately be calculated. In this work, the muon-nucleus integrals for a set of nuclei including the 28Si and 64Zn entering the ordinary muon capture rates are exactly obtained through numerical integrations using Gauss integration algorithms.