Showing papers in "Astrophysics and Space Science in 2019"

Hamilton’s approach in cosmological inflation with an exponential potential and its observational constraints

Abstract: The Friedmann-Robertson-Walker (FRW) cosmology is analyzed with a general potential $V(\phi)$ in the scalar field inflation scenario. The Bohmian approach (a WKB-like formalism) was employed in order to constraint a generic form of potential to the most suited to drive inflation, from here a family of potentials emerges; in particular we select an exponential potential as the first non trivial case and remains the object of interest of this work. The solution to the Wheeler-DeWitt (WDW) equation is also obtained for the selected potential in this scheme. Using Hamilton’s approach and equations of motion for a scalar field $\phi$ with standard kinetic energy, we find the exact solutions to the complete set of Einstein-Klein-Gordon (EKG) equations without the need of the slow-roll approximation (SR). In order to contrast this model with observational data (Akrami et al. 2018, arXiv:1807.06211 , (Planck Collaboration) results), the inflationary observables: the tensor-to-scalar ratio and the scalar spectral index are derived in our proper time, and then evaluated under the proper condition such as the number of e-folding corresponds exactly at 50–60 before inflation ends. The employed method exhibits a remarkable simplicity with rather interesting applications in the near future.

Observational constraints on the tilted flat-XCDM and the untilted nonflat XCDM dynamical dark energy inflation parameterizations

Abstract: We constrain tilted spatially-flat and untilted nonflat XCDM dynamical dark energy inflation parameterizations using Planck 2015 cosmic microwave background (CMB) anisotropy data and recent baryonic acoustic oscillations distance measurements, Type Ia supernovae data, Hubble parameter observations, and growth rate measurements. Inclusion of the four non-CMB data sets results in a significant strengthening of the evidence for nonflatness in the nonflat XCDM model from 1.1 $\sigma $ for the CMB data alone to 3.4 $\sigma $ for the full data combination. In this untilted nonflat XCDM case the data favor a spatially-closed model in which spatial curvature contributes a little less than a percent of the current cosmological energy budget; they also mildly favor dynamical dark energy over a cosmological constant at 1.2 $\sigma $ . These data are also better fit by the flat-XCDM parameterization than by the standard $\varLambda $ CDM model, but only at 0.3 $\sigma $ significance. Current data is unable to rule out dark energy dynamics. The nonflat XCDM parameterization is compatible with the Dark Energy Survey limits on the present value of the rms mass fluctuations amplitude ( $\sigma _{8}$ ) as a function of the present value of the nonrelativistic matter density parameter ( $\varOmega _{m}$ ). However, it does not provide as good a fit to the higher multipole CMB temperature anisotropy data as does the standard tilted flat- $\varLambda $ CDM model. A number of measured cosmological parameter values differ significantly when determined using the tilted flat-XCDM and the nonflat XCDM parameterizations, including the baryonic matter density parameter and the reionization optical depth.

Galaxy morphology classification with deep convolutional neural networks

Abstract: We propose a variant of residual networks (ResNets) for galaxy morphology classification. The variant, together with other popular convolutional neural networks (CNNs), is applied to a sample of 28790 galaxy images from the Galaxy Zoo 2 dataset, to classify galaxies into five classes, i.e., completely round smooth, in-between smooth (between completely round and cigar-shaped), cigar-shaped smooth, edge-on and spiral. Various metrics, such as accuracy, precision, recall, F1 value and AUC, show that the proposed network achieves state-of-the-art classification performance among other networks, namely, Dieleman, AlexNet, VGG, Inception and ResNets. The overall classification accuracy of our network on the testing set is 95.2083% and the accuracy of each type is given as follows: completely round, 96.6785%; in-between, 94.4238%; cigar-shaped, 58.6207%; edge-on, 94.3590% and spiral, 97.6953%. Our model algorithm can be applied to large-scale galaxy classification in forthcoming surveys, such as the Large Synoptic Survey Telescope (LSST) survey.

Planck 2015 constraints on spatially-flat dynamical dark energy models

Abstract: We determine constraints on spatially-flat tilted dynamical dark energy XCDM and $\phi $CDM inflation models by analyzing Planck 2015 cosmic microwave background (CMB) anisotropy data and baryon acoustic oscillation (BAO) distance measurements. XCDM is a simple and widely used but physically inconsistent parameterization of dynamical dark energy, while the $\phi $CDM model is a physically consistent one in which a scalar field $\phi $ with an inverse power-law potential energy density powers the currently accelerating cosmological expansion. Both these models have one additional parameter compared to standard $\varLambda $CDM and both better fit the TT + lowP + lensing + BAO data than does the standard tilted flat-$\varLambda $CDM model, with $\Delta \chi ^{2} = -1.26\ (-1.60)$ for the XCDM ($\phi $CDM) model relative to the $\varLambda $CDM model. While this is a 1.1$\sigma $ (1.3$\sigma $) improvement over standard $\varLambda $CDM and so not significant, dynamical dark energy models cannot be ruled out. In addition, both dynamical dark energy models reduce the tension between the Planck 2015 CMB anisotropy and the weak lensing $\sigma _{8}$ constraints.

Models of anisotropic compact stars in the Rastall theory of gravity

Abstract: In the present work, we have studied the anisotropic compact stars in the regime of Rastall theory using Karori and Barua $(\mathit{KB})$ type metric. For this investigation, we have considered three different known compact stars with anisotropic configuration namely, 4U 1820-30, Her X-1 and SAX J 1808.4-3658(SSI) with radii 10 km, 7.7 km and 7.07 km respectively. Formulation of field equations in this modified theory have also been presented. The unknown constants in KB metric have been obtained by using the matching of interior solution with the exterior vacuum solution. We investigate the various physical aspects of the presented model such as variation of energy density, energy conditions, hydrostatic equilibrium, stability, compactness and surface redshift. Graphical analysis of the variables involved in the obtained solution is also presented to observe their behavior more clearly. We also demonstrate the numerical values of some physical parameters in the tabular form by using the observational values of mass and radius. We also compute the numerical values of $\frac{2M}{R}$ using the presented model to check the Buchdahl limit for our system. The detailed analysis of matter variables revealed the regularity and stability of our proposed model.

Optical spectroscopic observations of gamma-ray blazar candidates VIII: the 2016–2017 follow up campaign carried out at SPM, NOT, KPNO and SOAR telescopes

Abstract: The third Fermi source catalog lists 3033 $\gamma $ -ray sources above $4\sigma $ significance. More than 30% are classified as either unidentified/unassociated Gamma-ray sources (UGSs), with about 20% classified as Blazar candidates of uncertain types (BCUs). To confirm the blazar-like nature of candidate counterparts of UGSs and BCUs, we started in 2012 an optical spectroscopic follow up campaign. We report here the spectra of 36 targets with observations from the Observatorio Astronomico Nacional San Pedro Martir, the Southern Astrophysical Research Observatory, the Kitt Peak National Observatory and the Northern Optical Telescope, between 2016 and 2017. We confirm the BL Lac nature of 23 sources, and the flat spectrum radio quasar nature of other 7 ones. We also provide redshift estimates for 19 out of these 30 confirmations, with only one being a lower limit due to spectral features ascribable to intervening systems along the line of sight. As in previous analyses, the largest fraction of now-classified BCUs belong to the class of BL Lac objects, that appear to be the most elusive class of active galactic nuclei. One of the BL Lacs identified in this work, associated with 3FGL J2213.6-4755, lies at a redshift of $z>1.529$ , making it one of the few distant gamma-ray BL Lac objects.

Measuring the Hubble constant and spatial curvature from supernova apparent magnitude, baryon acoustic oscillation, and Hubble parameter data

Abstract: Cosmic microwave background (CMB) anisotropy (spatial inhomogeneity) data provide the tightest constraints on the Hubble constant, matter density, spatial curvature, and dark energy dynamics. Other data, sensitive to the evolution of only the spatially homogeneous part of the cosmological model, such as Type Ia supernova apparent magnitude, baryon acoustic oscillation distance, and Hubble parameter measurements, can be used in conjunction with the CMB data to more tightly constrain parameters. Recent joint analyses of CMB and such non-CMB data indicate that slightly closed spatial hypersurfaces are favored in nonflat untilted inflation models and that dark energy dynamics cannot be ruled out, and favor a smaller Hubble constant. We show that the constraints that follow from these non-CMB data alone are consistent with those that follow from the CMB data alone and so also consistent with, but weaker than, those that follow from the joint analyses of the CMB and non-CMB data.

Shock waves and the formation of solitary structures in electron acoustic wave in inner magnetosphere plasma with relativistically degenerate particles

Abstract: The inner magnetosphere of Earth houses relativistically degenerate particles in which the formation of shocks and solitons occurs. In this paper we have considered plasma containing relativistically degenerate warm electrons and cold inertial electrons which give rise to electron acoustic solitary structure. We have also considered collisions which amount to dissipation actions and shocks. A KdV Burger equation has been derived by standard reductive perturbation technique and numerically analyzed by employing the celebrated Tan-hyperbolic method. The results are important in explaining the observed geo-magnetic storm in recent years.

Modeling and predicting seasonal ionospheric variations in Turkey using artificial neural network (ANN)

Abstract: The aim of this study was to model and predict seasonal ionospheric total electron content (TEC) using artificial neural network (ANN). Within this scope, GPS observations acquired from ANKR GPS station (Turkey) in 2015 were utilized to model TEC variations. Considering all data for each season, training and testing data were set as 80% and 10%, respectively, and the rest of the data were used to estimate TEC values using extracted mathematical models of ANN method. Day of Year (DOY), hour, F107 cm index (solar activity), Kp index and DsT index (magnetic storm index) were considered as the input parameters in ANN. The performances of ANN models were evaluated using RMSE and $R$ statistical metrics for each season. As a result of the analyses, considering the prediction results, ANN presented more successful predictions of TEC values in winter and autumn than summer and spring with RMSE 3.92 TECU and 3.97 TECU, respectively. On the other hand the $R$ value of winter data set (0.74) was lower than the autumn data set (0.88) while the RMSE values were opposite. This situation can be caused by the accuracy and precision of data sets. The results showed that the ANN model predicted GPS-TEC in a good agreement for ANKR station.

Ion acoustic cnoidal waves in a magnetized plasma in the presence of ion pressure anisotropy

Abstract: An investigation of the ion acoustic nonlinear periodic (cnoidal) waves in a magnetized plasma with positive ions having anisotropic thermal pressure and Maxwellian electrons is carried out. The Korteweg-de Vries equation for the wave potential is derived via a reductive perturbation technique and its cnoidal wave solution is obtained. The effect of various relevant plasma parameters like ion pressure anisotropy and obliqueness of field on the characteristics of ion acoustic nonlinear periodic wave structures is investigated in detail. The present investigation could be useful in space and astrophysical plasma systems having ion pressure anisotropy, particularly, in the magnetosphere and near Earth magnetosheath.

Optical spectroscopic observations of gamma-ray blazar candidates. IX. Optical archival spectra and further observations from SOAR and OAGH

Abstract: Nearly one third of the sources in the Fermi-LAT catalogs lacks a lower energy counterpart, hence being referred as unidentified/unassociated gamma-ray sources (UGSs). In order to firmly classify them, dedicated multifrequency follow-up campaigns are necessary. These will permit to unveil their nature and identify the fraction that could belong to the class of active galaxies known as blazars that is the largest population of extragalactic $\gamma $ -ray sources. In Fermi-LAT catalogs there are also gamma-ray sources associated with multifrequency blazar-like objects known as Blazars Candidates of Uncertain type (i.e., BCUs) for which follow up spectroscopic campaigns are mandatory to confirm their blazar nature. Thus, in 2013 we started an optical spectroscopic campaign to identify blazar-like objects potential counterparts of UGSs and BCUs. Here we report the spectra of 31 additional targets observed as part of our follow up campaign. Thirteen of them are BCUs for which we acquired spectroscopic observations at Observatorio Astrofisico Guillermo Haro (OAGH) and at Southern Astrophysical Research Observatory (SOAR) telescopes, while the rest has been identified thanks to the archival observations available from the Sloan Digital Sky Survey (SDSS). We confirm the blazar nature of all BCUs: three of them are in blazar of quasar type (BZQs) while the remaining ones can be spectroscopically classified as BL Lac objects (BZBs). Then we also discovered 18 BL Lac objects lying within the positional uncertainty regions of UGSs that could be their potential counterparts.

The periodic universe with varying deceleration parameter of the second degree

Abstract: In the present paper, we propose a new law for the deceleration parameter of the second degree of the time. Our law tells us about the behavior of the universe. According to our law, the spatially closed, flat and open universes are allowed, and the universe passes through with a big-rip and then retreats as it was in the moment of the big bang. The law we suggest covers the law of Berman, where the deceleration parameter is constant, also covers the law of the deceleration parameter of the first degree of time obtained by Akarsu and Tekin.

Dynamics of perfect fluid cosmological model in the presence of massive scalar field in f(R,T) gravity

Abstract: In this paper, we are interested to investigate spatially homogeneous and totally anisotropic perfect cosmological model in the presence of an attractive massive scalar field in $f(R,T)$ gravity in the background of Bianchi type- $\mathit{III}$ space-time. Here $R$ is the Ricci scalar and $T$ is the trace of the energy momentum tensor. In order to solve the field equations, we have used (i) the expansion scalar of the space-time is proportional to the shear scalar which leads to a relationship between metric potentials and (ii) a power law between the scalar field and the average scale factor. We obtain a cosmological model of the universe with variable deceleration parameter. We have computed all the cosmological parameters of the model and discussed their physical importance.

Whistler instability stimulated by the suprathermal electrons present in space plasmas

Abstract: In the absence of efficient collisions, deviations from thermal equilibrium of plasma particle distributions are controlled by the self-generated instabilities. The whistler instability is a notorious example, usually responsible for the regulation of electron temperature anisotropy $A = T_{\perp }/T_{\parallel }> 1$ (with $\perp , \parallel $ respective to the magnetic field direction) observed in space plasmas, e.g., solar wind and planetary magnetospheres. Suprathermal electrons present in these environments change the plasma dispersion and stability properties, with expected consequences on the kinetic instabilities and the resulting fluctuations, which, in turn, scatter the electrons and reduce their anisotropy. In order to capture these mutual effects we use a quasilinear kinetic approach and PIC simulations, which provide a comprehensive characterization of the whistler instability under the influence of suprathermal electrons. Analysis is performed for a large variety of plasma conditions, ranging from low-beta plasmas encountered in outer corona or planetary magnetospheres to a high-beta solar wind characteristic to large heliospheric distances. Enhanced by the suprathermal electrons, whistler fluctuations stimulate the relaxation of temperature anisotropy, and this influence of suprathermals increases with plasma beta parameter.

Properties of the black hole candidate XTE J1118+480 with the TCAF solution during its jet activity induced 2000 outburst

Abstract: The galactic black hole candidate (BHC) XTE J1118+480 during its 2000 outburst has been studied in a broad energy range using the archival data of PCA and HEXTE payloads of Rossi X-ray Timing Explorer. Detailed spectral and temporal properties of the source are studied. Low and very low frequency quasi-periodic oscillations (QPOs), with a general trend of increasing frequency are observed during the outburst. Spectral analysis is done using the combined data of the PCA and HEXTE instruments with two types of models: the well-known phenomenological power-law model and the current version of the fits file of two-component advective flow (TCAF) solution as an additive table model in XSPEC. During the entire period of the outburst, a non-thermal power-law component and the TCAF model fitted to the sub-Keplerian halo rate were found to be highly dominant. We suggest that this so-called outburst is due to enhanced jet activity. Indeed, the ‘outburst’ subsides when this activity disappears. We estimated the X-ray fluxes coming from the base of the jet and found that the radio flux is correlated with this X-ray flux. Though the object was in the hard state in the entire episode, the spectrum becomes slightly softer with the rise in the Keplerian disk rate in the late declining phase. We also estimated the probable mass of the source from our spectral analysis with the TCAF solution. Our estimated mass of XTE J1118+480 is $6.99^{+0.50}_{-0.74}~M_{\odot }$ i.e., in the range of 6.25– $7.49~M _{\odot }$ .

A hybrid ensemble method for pulsar candidate classification

Abstract: In this paper, three ensemble methods: Random Forest, XGBoost, and a Hybrid Ensemble method were implemented to classify imbalanced pulsar candidates. To assist these methods, tree models were used to select features among 30 features of pulsar candidates from references. The skewness of the integrated pulse profile, chi-squared value for sine-squared fit to amended profile and best S/N value play important roles in Random Forest, while the skewness of the integrated pulse profile is one of the most significant features in XGBoost. More than 20 features were selected by their relative scores and then applied in three ensemble methods. In the Hybrid Ensemble method, we combined Random Forest and XGBoost with EasyEnsemble. By changing thresholds, we tried to make a trade-off between Recall and Precision to make them approximately equal and as high as possible. Experiments on HTRU 1 and HTRU 2 datasets show that the Hybrid Ensemble method achieves higher Recall than the other two algorithms. In HTRU 1 dataset, Recall, Precision, and F-Score of the Hybrid Ensemble method are 0.967, 0.971, and 0.969, respectively. In HTRU 2 dataset, the three values of that are 0.920, 0.917, and 0.918, respectively.

Bifurcation of ion-acoustic superperiodic waves in auroral zone of Earth’s magnetosphere

Abstract: Ion-acoustic (IA) superperiodic waves are explored in an unmagnetized plasma composing of mobile ions, Maxwell distributed cold electrons and non-thermal hot electrons. Implementing the phase portrait concept of the Hamiltonian systems, all distinct phase plots containing superperiodic and superhomoclinic trajectories are displayed for distinct data values of the physical parameters, such as, nonthermal parameter ($\beta $), number density ratio ($\mu $) of cold electrons and ions at equilibrium, temperature ratio ($\sigma $) of cold electrons to hot electrons and of traveling wave velocity ($v$). The IA superperiodic wave features are examined for various conditions of physical parameters by symbolic computations. The outcomes of this study may be beneficial in discerning IA superperiodic wave in auroral zone of the Earth’s magnetosphere.

Low-latitude ionospheric response from GPS, IRI and TIE-GCM TEC to Solar Cycle 24

Abstract: In the present study inter-comparison of Total Electron Content (TEC) derived from the Global Positioning System, the International Reference Ionosphere (IRI-2016) model and the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) during Solar Cycle 24 has been carried out. The short- and long-term variabilities in TEC have been assessed by using spectral, regression and statistical analysis. To ascertain the quiet-time climatology, TEC data have been used after filtering out the solar flares and geomagnetic storms effects. The present analysis exhibits a double-hump structure and clockwise hysteresis in TEC as regards Solar Cycle 24. The solar flux and TEC trend are found to be irregularly and slow during the rise and smooth and quick during the fall period of Solar Cycle 24. Seasonally, the semiannual anomaly is found to be a consistent feature for all phases of the solar cycle, while the winter anomaly seems to be facilitated with a level of solar activity during solstices. Another purpose of the present work is to investigate the performance of IRI-2016 and the TIE-GCM 2.0 models in comparison with GPS-TEC during Solar Cycle 24. Almost perfect agreement is found between observed and modeled TEC, delineating similar trends of the solar cycle, and of semiannual and seasonal variations. Nevertheless, significant biases are apparent between the observed and modeled TEC in terms of local time, seasons and phases of solar activity. Our results show the error in the model estimations in noontime TEC, which is as high as 100% in the IRI model and as low as 60% in the TIE-GCM model. Thus, in general, the IRI model overestimates the noon time TEC values, while TIE-GCM underestimates them.

Relativistic model for anisotropic compact stars using Karmarkar condition

Abstract: In this work we have obtained some families of relativistic anisotropic compact stars by solving of Einstein’s field equations. The field equations have been solved by suitable particular choice of the metric potential $e^{\lambda }$ and embedding class one condition. The physical analysis of this model indicates that the obtained relativistic stellar structure for anisotropic matter distribution is physically reasonable model for compact star whose energy density of the order $10^{15}~\mbox{g}/\mbox{cm}^{3}$ . Using the Tolman-Oppenheimer-Volkoff equations, we explore the hydrostatic equilibrium and the stability of the compact stars like PSR J1614-2230, 4U 1608-52, SAX J1808.4-3658, LMC X-4, RX J1856-37, Vela X-1, 4U 1820-30, EXO 1785-248, PSR J1903+327, 4U 1538-52, SMC X-1, Her X-1 and Cen X-3. We also estimated the mass and radius of such compact stars.

Prediction of declining solar activity trends during solar cycles 25 and 26 and indication of other solar minimum

Abstract: Study of variations in solar activity parameters has its importance in understanding the underlying mechanisms of space weather phenomena and space climate variability. We have used the already observed data of solar parameters viz. sunspot numbers, F10.7 cm index and Lyman alpha index recorded for last seventy years (1947–2017). We have applied the Hodrick Prescott filtering method to bifurcate each time series into cyclic and trend parts. The cyclic part of each time series was used to analyse the persistence while the trend part was used to obtain the input data for the study of future predictions. Further, the cyclic component of each parameter was analysed by using the rescaled range analysis and the value of Hurst exponent was obtained for sunspot numbers, F10.7 cm index and Lyman alpha index as 0.90, 0.93 and 0.96 respectively. By using the simplex projection analysis on the values of amplitude and phase of the trend component of each time series, we have reconstructed the future time series representing solar cycles 25 and 26. When extrapolated further in time, the reconstructed series provided the maximum values of sunspot numbers as $89 \pm 9$ and $78 \pm 7$ ; maximum values of F10.7 cm index were $124 \pm 11$ and $118 \pm 9$ and Lyman alpha index were $4.61 \pm 0.08$ and $4.41 \pm 0.08$ respectively for solar cycles 25 and 26. In our analysis we have found that the solar cycle 25 will start in the year 2021 (January) and will last till 2031 (February) with its maxima in year 2024 (February) while the solar cycle 26 will start in the year 2031 (March) with its maxima in 2036 (June) and will last till the year 2041 (February). We have also compared the activities of solar cycles 5 and 6 (Dalton minima periods) to solar cycles 25 and 26 and have observed that the other solar minimum is underway.

Charged compact star model in Einstein-Maxwell-Gauss-Bonnet gravity

Abstract: In this paper we present a model of a static charged anisotropic fluid sphere in the Einstein-Maxwell-Gauss-Bonnet (EMGB) theory of gravitation. We utilize the Krori-Barua (KB) ansatz together with a linear equation of state of the form $p_{r}=\beta \rho -\gamma $ to generate exact solutions of the EMGB field equations describing compact objects. The model obtained here is found to satisfy the elementary physical requirements necessary for a physically realizable stellar object. We demonstrate that contributions from the Gauss-Bonnet terms have a nonzero impact on the density, pressure and anisotropy profiles. The vanishing of the electromagnetic field at the center of the stellar configuration leads to a relation between the equation of state parameter and the Gauss-Bonnet term. Our model reveals a direct connection between the nature of the matter configuration and higher dimensional effects.

Charged gravastars with conformal motion in f (R,T ) gravity

Abstract: This paper studies the effects of charge on a peculiar stellar object, recognized as gravastar, under the influence of $f(R,T)$ gravity by considering the conjecture of Mazur and Mottola in general relativity. The gravastar is also known as an alternative to a black hole and is expressed by three distinct domains named as (i) the interior domain, (ii) the intermediate shell and (iii) the exterior domain. We analyze these domains for a specific $f(R,T)$ gravity model conceding the conformal Killing vectors. In the interior domain, we assume that pressure is equal to negative energy density which leads to the existence of repulsive force on the spherical shell. The intermediate shell consists of ultra-relativistic plasma and pressure which shows a direct relation with energy density and counterbalances the repulsive force applied by the interior domain. The exterior vacuum spherical domain is taken to be the de Sitter spacetime illustrated by the Reissner-Nordstrom metric. We conclude that non-singular solutions of charged gravastar with various physical properties such as length, energy, entropy and equation of state parameter are physically consistent.

Linearized stability of Bardeen anti-de Sitter wormholes

Abstract: In this paper, we explore the stable and unstable geometrical structures of thin-shell wormholes. We use Visser cut and paste approach to develop thin-shell from Bardeen anti-de Sitter black holes. The characteristics of matter distribution are determined by using Israel formalism. We discuss the existence of exotic matter at the wormhole throat through energy conditions and examine the attractive/repulsive nature of wormhole throat. The linearized stability of thin-shell is studied through barotropic and variable equations of state (generalized phantomlike and generalized Chaplygin gas model). We conclude that the stability of wormhole depends on the matter distribution as well as cosmological constant. Finally, we compare the stable structure of wormhole for these equations of state through length parameter.

Kaluza-Klein dark energy model in Lyra manifold in the presence of massive scalar field

Abstract: In this investigation we intend to study the dynamics of an anisotropic dark energy cosmological model in the presence of a massive scalar field in a modified Riemannian manifold proposed by Lyra (Math. Z. 54:52, 1951) in the background of a five dimensional Kaluza-Klein space time. We solve the Einstein field equations using some physically significant conditions and present a deterministic dark energy cosmological model. We use here the time dependent displacement vector field of the Lyra manifold. All the dynamical parameters of the model, namely, average Hubble parameter, anisotropy parameter, equation of state parameter, dark energy density, deceleration parameter and statefinders are evaluated for our model and their physical relevance to modern cosmology is discussed in detail.

The effect of small perturbations in the Coriolis and centrifugal forces in the axisymmetric restricted five-body problem

Abstract: In the framework of the axisymmetric problem of restricted five bodies, the existence and stability of the libration points, the regions of possible motion are illustrated and analyzed numerically, under the effect of small perturbations in the Coriolis and centrifugal forces. It is explored how the parameters influence substantially the positions of the libration points and the possible regions of motion. In an attempt to understand how the parameters involved due to the small perturbations in the Coriolis and centrifugal forces affect the stability of the libration points, we perform a systematic investigation and reveal that some of the collinear and non-collinear libration points are stable under these perturbations, whereas none of these libration points are stable for any combination of the angle parameters when the effects of these forces are neglected.

Ionospheric monitoring system based on the Internet of Things with ThingSpeak

Abstract: The Internet of Things (IoT) is a growing technology that allows digital devices to be integrated into the network. The use of IoT technology makes it possible to collect information from various Global Navigation Satellite System (GNSS) receivers connected to the Internet, providing a unique opportunity to obtain information on spatial and temporal distribution. In this article, the ionospheric monitoring system is implemented using ThingSpeak (IoT). Ionospheric signal delay/Total Electronic Content (TEC) data from GNSS stations, Koneru Lakshmaiah Education Foundation (KLEF)—Guntur (16.44° N, 80.62° E, geographical), Port Blair (11, 43° N, 92,43° E)—geographical, Bengaluru (13,02° N, 77,57° E; geographical), Lucknow (26,76° N, 80,88° E; geographical) are used for analysis during the 2015 period. The ionospheric signal delays are computed from the ThingSpeak and the ionospheric TEC analysis are performed directly in the MATLAB software. The computed observed TEC values were compared to the IRI-16 (International Reference Ionosphere) model values. The standard deviation of the observed TEC for four GNSS stations is 17.26 TECU for Port Blair, 18.34 TECU for Bengaluru, 16.51 TECU for KLEF-Guntur and 14.07 TECU for Lucknow. The corresponding standard deviation of the IRI model is 11.38 TECU for Port Blair, 13.25 TECU for Bengaluru, 17.67 TECU for KLEF-Guntur and 15.66 TECU for Lucknow. As a result, the cloud-based monitoring system reduces operating costs, backs up and retrieves data. It optimizes productivity and collaboration around the world via the Internet.

Thermodynamics and stability of f(T,B) gravity with viscous fluid by observational constraints

Abstract: In this paper, we study the model of $f(T, B)$ gravity with viscous fluid in flat-FRW metric, in which $T$ and $B$ are torsion scalar and boundary term, respectively. We obtain the Friedmann equations in the framework of modified teleparallel gravity by tetrad components. We consider an interacting model between matter and dark energy so that universe dominates by viscous fluid. Then, we write the corresponding cosmological parameters in terms of the redshift parameter, and, we parameterize the Hubble parameter with experimental data. In what follows, we plot the corresponding cosmological parameters for dark energy components in terms of redshift, thereafter we investigate the accelerated expansion of the universe. Moreover, we discuss the stability of the model by using the sound speed parameter. Finally, we investigate the validity of the generalized second law of thermodynamics.

Bulk viscous string cosmological models in Saez-Ballester theory of gravity

Abstract: In this communication, a new class of bulk viscous string cosmological models has been constructed in Saez-Ballester theory of gravitation. To obtain the deterministic solution of the field equations, we have considered deceleration parameter as a bilinear function of cosmic time $t$ for model I and special parametrization of Hubble parameter for model II. The presented class of the cosmological models indicate phase conversion from early decelerated expansion phase to present accelerated expansion phase. To discuss the dynamicity of the universe, the behaviour of various physical parameters has also been studied and presented graphically. For stability analysis, the nature of various energy conditions is investigated. Statefinder pair analysis is used to discriminate the constructed models with other dark energy models and it is noticed that the proposed models are in good agreement with recent observational data.

Solving procedure for 3D motions near libration points in CR3BP

Abstract: In a novel approach for solving the equations of the Circular Restricted Three-Body Problem (CR3BP) first formulated in Ershkov (Acta Mech. 228(7):2719–2723, 2017a), we apply in this communication a procedure for solving the Euler-Poisson equations for the momentum equations of the CR3BP near the libration points for uniformly rotating planets having inclined orbits in the solar system with respect to the orbit of the Earth. The system of equations of the CR3BP has been explored with regard to the existence of an analytic way of presentation of the approximated solution in the vicinity of libration points. A new and elegant ansatz is suggested in this publication, whereby, in solving, the momentum equation is reduced to a system of three linear ordinary differential equations of first order in regard to the three components of the velocity of the infinitesimal mass $m$ (dependent on time $t$ ). Under this premise, a proper elegant partial solution has been obtained due to the invariant dependence between temporary components of the solution. We conclude that the system of CR3BP equations does not have the analytical presentation of the solution (in quadratures) even in the vicinity of the libration points except of the generalized Jacobi integral.

Combined effect of Stokes drag, oblateness and radiation pressure on the existence and stability of equilibrium points in the restricted four-body problem

Abstract: This paper studies numerically the existence of collinear and non-collinear equilibrium points and their linear stability in the frame work of photogravitational circular restricted four-body problem with Stokes drag acting as a dissipative force and considering the first primary as a radiating body and the second primary as an oblate spheroid. The mass of the fourth body is assumed to be infinitesimal and does not affect the motion of the three primaries which are always at the vertices of an equilateral triangle (Lagrangian configuration). It is found that at constant dissipative force, and a simultaneous increase in both radiation pressure and oblateness coefficients, the curves that define the path of the motion of the infinitesimal body are found to shrink due to shifts in the positions of equilibrium points. All the collinear and non-collinear equilibrium points are found to be linearly unstable under the combined effect of radiation pressure, oblateness and Stokes drag. The energy integral is seen to be time dependent due to the presence of the drag force. More so the dynamic property of the system is investigated with the help of Lyapunov characteristic exponents (LCEs). It is found that the system is chaotic as the trajectories locally diverge from each other and the equilibrium points are chaotic attractors. We justified the relevance of the model in astronomy by applying it to a stellar system (Gliese 667C) and another found that both the existence and stability of the equilibrium points of any restricted few body system greatly depend of the value of the mass parameter.