bluuebunny/crossref_metadata_2025_split huggingface dataset:
The relaxation of galaxy clusters at redshift z = 0 in IllustrisTNG simulation
Authors: Li Chao , Zhu Ling , Guo Rui 
Published: January 2021

Abstract
We study the dynamical states of the 30 most massive galaxy clusters in the TNG100 simulation at redshift z = 0 using three types of tracers: stars, dark matter particles and satellite galaxies. If the massive galaxy cluster is spherically symmetric and relaxed, we can obtain the underlying total mass distribution accurately from its dynamical tracers using the spherical Jeans equations. Although the three tracers of clusters have very different number densities, velocity dispersions and anisotropies, they still trace the same total mass profile. We obtain the total mass profiles of clusters using these tracers separately and compare them with the true mass distributions. We find that: (1) the kinematics of dark matter trace the total mass of all clusters well and the mass inferred from dark matter are generally consistent with the true mass profiles with relative deviations smaller than ∼ 25% at all radii; (2) stars in ∼ 60% massive clusters are approaching equilibrium and the total mass of these clusters inferred from stars have relative deviations smaller than ∼ 50% at all radii. Stellar substructures are rich and the mass inferred from stars tend to be over-estimated in the inner region; and (3) satellite galaxies are unrelaxed in the inner region and become more relaxed as the radius increases. The total mass inferred from satellites are under-estimated in all regions.
A photometric-spectroscopic study of the infrared-excess eclipsing binary V2364 Cyg
Authors: Yuan Hui-Yu , Jiang Lin-Qiao , Dai Hai-Feng , Wang Shuang , Yang Yuan-Gui 
Published: January 2021

Abstract
The eclipsing binary V2364 Cyg is an A7V-type contact binary with a period of 0.5921 d. We present six spectra from LAMOST and BVRc
light curves (LCs), which are simultaneously analyzed to obtain the absolute physical parameters. The first light maxima are brighter than the second ones by up to

0
.
m

038

,

0
.
m

036

and

0
.
m

024

for BVRc
bands, respectively. These distorted LCs are modeled by a cool spot on the less massive component. Its mass ratio and over-contact degree are q = 0.319(±0.004) and f = 28.4%(±1.0)% respectively. From the mass-luminosity diagram, the primary component is a normal main-sequence star, while the secondary one is a subgiant star. From the (O – C) curve, the orbital period secularly decreases at a rate dP/dt = –1.62(±0.03)×10−7d yr−1, which is mainly attributed to mass loss via stellar wind from the binary system. This may result in the observed infrared excess in the W4 band.
Generating a radioheliograph image from SDO/AIA data with the machine learning method
Authors: Zhang Pei-Jin , Wang Chuan-Bing , Pu Guan-Shan 
Published: January 2021

Abstract
Radioheliograph images are essential for the study of solar short term activities and long term variations, while the continuity and granularity of radioheliograph data are not so ideal, due to the short visible time of the Sun and the complex electron-magnetic environment near the ground-based radio telescope. In this work, we develop a multi-channel input single-channel output neural network, which can generate radioheliograph image in microwave band from the Extreme Ultra-violet (EUV) observation of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO). The neural network is trained with nearly 8 years of data of Nobeyama Radioheliograph (NoRH) at 17 GHz and SDO/AIA from January 2011 to September 2018. The generated radioheliograph image is in good consistency with the well-calibrated NoRH observation. SDO/AIA provides solar atmosphere images in multiple EUV wavelengths every 12 seconds from space, so the present model can fill the vacancy of limited observation time of microwave radioheliograph, and support further study of the relationship between the microwave and EUV emission.
Combined limit on the photon mass with nine localized fast radio bursts
Authors: Wei Jun-Jie , Wu Xue-Feng 
Published: January 2021

Abstract
A nonzero-mass hypothesis for the photon can produce a frequency-dependent dispersion of light, which results in arrival-time differences of photons with different frequencies originating from a given transient source. Extragalactic fast radio bursts (FRBs), with their low frequency emissions, short time durations, and long propagation distances, are excellent astrophysical probes to constrain the rest mass of the photon mγ
. However, the derivation of a limit on mγ
is complicated by the similar frequency dependences of dispersion expected from the plasma and nonzero photon mass effects. If a handful measurements of redshift for FRBs are available, then the different redshift dependences of the plasma and photon mass contributions to the dispersion measure (DM) might be able to break dispersion degeneracy in testing the photon mass. For now, nine FRBs with redshift measurements have been reported, which can turn this idea into reality. Taking into account the DM contributions from both the plasma and a possible photon mass, we use the data on the nine FRBs to derive a combined limit of mγ
≤ 7.1 × 10−51 kg, or equivalently mγ
≤ 4.0 × 10−15 eV/c
2 at 68 % confidence level, which is essentially as good as or represents a factor of 7 improvement over previous limits obtained by the single FRBs. Additionally, a reasonable estimation for the DM contribution from the host galaxy, DMhost, can be simultaneously achieved in our analysis. The rapid progress in localizing FRBs will further tighten the constraints on both mγ
and DMhost.
Spectral analysis of χ class data of GRS 1915+105 using TCAF solution
Authors: Banerjee Anuvab , Bhattacharjee Ayan , Debnath Dipak , Chakrabarti Sandip K. 
Published: January 2021

Abstract
The class variable source GRS 1915+105 exhibits a wide range of time variabilities on timescales of a few seconds to a few days. Depending on the count rates in different energy bands and the nature of the conventional color-color diagram, the variabilities were classified into sixteen classes that were later sequenced in ascending order of Comptonization Efficiency (CE), which is the ratio of power-law and blackbody photons. However, CE estimation is based on an empirical model which does not provide us with a comprehensive picture regarding accretion flow dynamics around the central source. In reality, the accretion flow is comprised of two components: the high angular momentumKeplerian flow in the form of a radiatively efficient disk and a low angular momentumradiatively inefficient sub-Keplerian halo enveloping the disk. These two components contribute differently to the overall flux due to the differences in their radiative efficiencies. Therefore, it is necessary to analyze the spectral behaviors and time variabilities in terms of accretion rates. In χ class, X-ray flux is steady with no significant variation, however various χ subclasses are observed at different X-ray fluxes and variations of count rates across different χ subclasses must be linked to the variation of flow parameters such as the accretion rates, be it the Keplerian disk rate and/or the low angular momentum halo rate. This motivated us to analyze the spectra of the χ class data implementing the physical Two Component Advective Flow (TCAF) solution which directly extracts these two rates from spectral fits. We find that in the χ
2,4 classes, which are reportedly devoid of significant outflows, the spectra could be fitted well applying the TCAF solution alone. In the χ
1,3 classes, which are always linked with outflows, a cutoff power-law model is needed in addition to the TCAF solution. At the same time, the normalization required by this model along with the variation of photon index and exponential roll-off factor provides us with information on the relative dominance of the outflow in the latter two classes. TCAF fit also supplies us with the size and location of the Compton cloud along with its optical depth. Thus by fitting with TCAF, a physical understanding of the flow geometry in different χ classes of GRS 1915+105 has been obtained.
On the possible orbital motion of Sgr A* in the smooth potential of the Milky Way
Authors: Nikiforov Igor’ I. , Veselova Angelina V. 
Published: January 2021

Abstract
The modern accuracy of measurements allows the residual/peculiar (Galactocentric) velocity of the supermassive black hole (SMBH) in our Galaxy, Sgr A*, on the order of several kilometers per second. We integrate possible orbits of the SMBH along with the surrounding nuclear stellar cluster (NSC) for a barred model of the Galaxy using modern constraints on the components of the SMBH Galactocentric velocity. Is is shown that the range of oscillations of the SMBH+NSC in a regular Galactic field in the plane of the Galaxy allowed by these constraints strongly depends on the set of central components of the Galactic potential. If the central components are represented only by a bulge/bar, for a point estimate of the SMBH Galactocentric velocity, the oscillation amplitude does not exceed 7 pc in the case that a classical bulge is present and reaches 25 pc if there is no bulge; with SMBH velocity components within the 2σ significance level, the amplitude can reach 15 and 50 pc, respectively. However, when taking into account the nuclear stellar disk (NSD), even in the absence of a bulge, the oscillation amplitude is only 5 pc for the point estimate of the SMBH velocity, and 10 pc for the 2σ significance level. Thus, the possible oscillations of the SMBH + NSC complex from the confirmed components of the Galaxy’s potential are mostly limited by the NSD, and even taking into account the uncertainty of the mass of the latter, the oscillation amplitude can hardly exceed 13 pc = 6′.
Development of machine learning techniques to enhance turbulence models
Authors: Razizadeh O , Yakovenko S N 
Published: January 2021

Abstract
The implementation of the machine learning methods of convolutional neural networks to enhance RANS closure models is presented. The RANS models are not universal and accurate, however they are computationally affordable. Finding a way to improve the model predictability will be an advantage. For this, machine learning algorithms based on available high-fidelity data sets for canonical flow cases obtained from DNS and measurements can be helpful. The application of these algorithms for a fully-developed turbulent channel flows with periodic hills, in a square duct and for other cases is considered.
Identification of connected arguments based on reasoning schemes “from expert opinion”
Authors: Salomatina N V , Kononenko I S , Sidorova E A , Pimenov I S 
Published: January 2021

Abstract
The work presented describes a combined approach to the partial extraction of the argumentative structure of a text that can be employed in the absence of sufficient annotated data to apply efficiently the machine learning methods for the direct detection of arguments and their relations. In this case, argument identification is performed by using the patterns of argumentation indicators created by a linguist and automatically expanded. These patterns enable the recognition of specific argument types with fine precision. In this study, arguments “from expert opinion” serve as such a pivot type. Besides, potential relations between recognized arguments are analyzed by dividing the text into superphrasal units (fragments united by one topic). The criterion for connecting arguments in an argumentative structure is their inclusion in the same superphrasal unit. An experiment for identifying potentially related arguments is conducted on a set of popular science texts with a minimum size of 1000 words.
The influence of the magnetic field on the quasistationary electric field penetration from the ground to the ionosphere
Authors: Nesterov S A , Denisenko V V 
Published: January 2021

Abstract
A quantitative model of the penetration of a quasistationary electric field from the Earth’s surface into the ionosphere with an inclined magnetic field has been developed. The results of the three-dimensional model are simpler regarding interpretation and explanation than those dimensional ones. The electric conductivity problem is solved using Fourier transform at each height. The space distributions of the electric field strength and the current density are calculated. The current lines are plotted. The electric field strength in the ionosphere is in the microvolt per meter range when it is about 100 V/m in the air near ground. The known approximate estimates of decrease in the electric field penetrating into the ionosphere with decrease in the magnetic latitude are confirmed and detailed. The penetration of the electric field and currents from the ground to the ionosphere through the atmospheric conductor cannot be a physical process which creates the observed ionospheric precursors of the earthquakes.
Solving of an Inverse Boundary Value Problem for the Heat Conduction Equation by Using Lavrentiev Regularization Method
Authors: Al-Mahdawi H K 
Published: January 2021

Abstract
In this paper, the inverse problem for the boundary value of the heat equation is posed and solved. It is well known that this problem classified as an ill-posed problem. The boundary value problem can be represented as an integral equation of the first kind by using the separation of variables method. The discretization of the integral equation allowed us to reduce the integral equation to a system of linear algebraic equations or a linear operator equation of the first kind on Hilbert spaces. In order to find an approximation solution, we need to apply a regularization algorithm. In this type of equation and through the regularization step we faced a non-injective operator problem. The Lavrentev regularization method was used to obtain the solution instead of the Tikhonov regularization method.
Comparative analysis of methods of recovering the well flow-rate and water-cut by thermodynamic measurements
Authors: Kabanikhin Sergey , Prikhodko Aleksei , Shishlenin Maxim 
Published: January 2021

Abstract
An important problem of oil well diagnostics is to quickly determine changes in the amount of liquid entering the well (flow rate), and the ratio of the amount of water to the amount of liquid (water cut). To calculate these parameters, thermodynamic measurements (temperature, pressure) can be used at the wellhead and downhole of the well, as well as garlands at the wellhead of sensors 10-20 meters long, with a frequency of 1 meter, for more information. The article presents a comparative analysis of algorithms for determining these parameters based on the solution of the inverse problem. The results of numerical calculations are presented.
Applicability of the single-scattering approximation for the ocean acoustic sounding
Authors: Vornovskikh P A , Prokhorov I V 
Published: January 2021

Abstract
A mathematical model in the work that describes the process of pulsed high-frequency acoustic sounding in a fluctuating ocean is considered. The inverse problem for the non-stationary equation of acoustic radiative transfer is investigated. It consists in finding the coefficient of volume scattering from the angular distribution of the radiation flux density at a given point in space. In the single scattering approximation, a formula is obtained to find the scattering coefficient. A series of computational experiments was carried out to substantiate its use in acoustic sensing of a fluctuating water medium. A numerical analysis has shown that the application of the single scattering approximation is justified at least at a sensing range of the order of 100 meters. Moreover, double and triple scattered fields have the main effect on the error.
Numerical modeling results of vibroseismic monitoring of volcanic structures with different shape of the magma chamber
Authors: Sapetina A F , Glinskiy B M , Martynov V N 
Published: January 2021

Abstract
The paper considers the possibility of active monitoring of volcanic structures based on the simulation of vibroseismic transmission using the dynamical theory of elasticity. A solution method, a parallel algorithm, and a program system based on a finite-difference approach together with CFS-PML method of absorbing boundaries are developed. Different variations of a magmatic stratovolcano approximate model are considered, comparative numerical calculations are carried out. The calculated wave field inside the volcanic structure has a compound structure depending on the geometry of studied objects and their rheological characteristics. Based on the studies, it may be concluded that monitoring of the considered type of volcanoes using precision vibroseismic sources and seismic observation systems is possible. A variant of vibroseismic monitoring of Elbrus volcano using the observation system in the tunnel of the Baksan Neutrino Observatory is proposed.
Iterative methods for solving Riccati differential equations
Authors: Ogundile O. P. , Edeki S. O. , Olaniregun D. G. 
Published: January 2021

AbstractThis work considers the approximate solution of the Riccati differential equations (RDEs). For ease of computation, the iterative methods applied are the Daftardar-Gejji and Jafari Method (DJM) and the Picard Iteration Method (PIM). The results obtained via the DJM are compared with those from PIM. The comparison shows that both methods are in agreement with the corresponding exact form. The Picard approach transforms the differential equation into an interconnected form; though, Lipschitz’s criterion of consistency but satisfied.
Remarks on the solution of a one-dimensional heat model with axial symmetry using decomposition method
Authors: Edeki S. O. , Abolarinwa A. , Ogundile O. P. , Ogunniyi P. O. 
Published: January 2021

Abstract
This paper explores the use of a new decomposition method termed-Natural Decomposition Method (NDM) on a one-dimensional heat model-equation with axial symmetry for analytical solutions. The series solutions of the sampled cases are obtained by the proposed method with ease and high precision for less computational time. Hence, this indicates the feasibility of the proposed approach.
Factors affecting the study time of first and final year students of a world class university
Authors: Okagbue Hilary I. , Odetunmibi Oluwole A. , Ezenkwe Adaeze M. , Anene Glory N. , Boluwajoko Anjoreoluwa E. , Offiah Ifeanyi B. , Akinsola Boluwatife E. 
Published: January 2021

Abstract
Many activities compete for the time students spent on academic activities, but few works have been done on the factors affecting the study times of first and final year students. Questionnaires were given to 150 first and final year students from four colleges of a world-class university located in Ogun State, Nigeria and the aim is to investigate the factors affecting their study time. Ninety-eight representing 65.3% of the students study between 1 and 4 hours per day. Gender, age, level and college affiliation are not associated with their perceived desired results. In the same vein, it was observed that gender and age are not associated with hours of study. However, there are significant associations between the duo of level and college and study hours. Also, there is no significant association (i) Between the number of hours spent on sleeping and the number of hours spent on studying and (ii). The hours spent on study and the desired result. In conclusion, strategies are needed to be crafted and deployed to increase the hours spent on studying by the first and final year students which are likely to give them their desired results and improve the art of learning. Logistic regression on the desired results was predicted by the 3 moderation variables, namely; the gender and level, age and college, and level and college. Intervention programmes are to be incorporated into the curriculum to motivate students in achieving their desired results. Tutorial classes, investment in learning tools, promotion of discussion groups, counselling are recommended for first and final year students to stimulate their interests in their chosen course of study and to prepare them for successful careers.
The relevance of the internet of things to the real estate profession
Authors: Akindele N. A. , Ogundile O. P. , Ogunniyi P. O. 
Published: January 2021

Abstract
This paper examines the relevance of the Internet of Things to the Real Estate profession. Questionnaires were distributed, and the interview was also conducted on the Estate Surveyors and Valuers in Akure metropolis. The paper adopts a quantitative method of data analysis. Descriptive techniques were adopted; it includes the tabular analysis of data using percentages and frequencies. A bar chart and Pie chart were also used. From table 4 and figure one (1) (bar chart), it was discovered that most of the respondents are aware of the existence of the Internet of Things as the majority of them indicated their awareness. Table 5 and figure 2 (Pie chart) also show that a high percentage of the respondents agreed that the Internet of Things is relevant to the Real Estate profession.
Enhanced Numerov Method for the Numerical Solution of Second Order Initial Value Problems
Authors: Akinlabi G. O. , Bishop S. A. , Edeki S. O. 
Published: January 2021

AbstractNumerov method is a multistep numerical method that is used in solving second order differential equations. In this work, we apply this method as a Boundary Value Method (BVM) for the numerical approximation of both linear and nonlinear second order initial value problems. This is achieved by constructing the Numerov method via interpolation and collocation process while utilizing data at off-step points and implementing it as a BVM. On comparing the results obtained from the solved problems, it shows that the method is accurate with high level of convergence to their exact forms and performs better than results from literature.
Trend Analysis of the Variations of Ambient Temperature Using Mann-Kendall Test and Sen’s Estimate in Calabar, Southern Nigeria
Authors: Agbo E P , Ekpo C M 
Published: January 2021

Abstract
Studies have been made to understand the fluctuations of temperature in regions around the world because of an ever changing variation due mostly to man’s anthropogenic activities. This study is focused on analysing the temperature variations in Calabar, Southern Nigeria for 20 years (1998 – 2018) using the Mann-Kendall trend test and Sen’s slope estimator. Results from the Mann-Kendall test shows that the annual trends of the maximum and average ambient temperature are both increasing after showing positive Kendall Z-values (1.04 and 0.10 respectively). The minimum ambient temperature annual trend was observed to be decreasing after having a negative Kendall Z-value (-0.32); the estimations from Sen’s slope agreed with these results. The p-values were calculated to be 0.745, 0.299, and 0.922 for the minimum, maximum, and average ambient temperature trend respectively; these values were all found to be less than all significant levels used 0.1% (0.001), 1% (0.01), 5% (0.05), and 10% (0.1). This shows that the trends were not increasing or decreasing significantly, hence there is “no significant trend”. This may be due to the almost unchanging weather condition in the region arising from its closeness to the Atlantic Ocean.