Advances in Astronomy最新文献

{"title":"A Study of the Early Cosmic Dynamics in a Multifield Model of Inflation and Curvature Perturbations","authors":"Muhammad Zahid Mughal, Feroz Khan, Fuad A. Awwad, Emad A. A. Ismail","doi":"10.1155/2024/8446071","DOIUrl":"https://doi.org/10.1155/2024/8446071","url":null,"abstract":"In this work, we study the cosmological dynamics of the early universe by employing a small field potential in the context of multifield inflation. By investigating analytically the cosmological observables, such as the number of e-folds <span><svg height=\"8.8423pt\" style=\"vertical-align:-0.2064009pt\" version=\"1.1\" viewbox=\"-0.0498162 -8.6359 11.0475 8.8423\" width=\"11.0475pt\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\"><g transform=\"matrix(.013,0,0,-0.013,0,0)\"></path></g></svg>,</span> potential slow-roll parameters <span><svg height=\"9.25202pt\" style=\"vertical-align:-3.29111pt\" version=\"1.1\" viewbox=\"-0.0498162 -5.96091 12.3625 9.25202\" width=\"12.3625pt\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\"><g transform=\"matrix(.013,0,0,-0.013,0,0)\"></path></g><g transform=\"matrix(.0091,0,0,-0.0091,5.187,3.132)\"></path></g></svg>,</span> <span><svg height=\"9.39034pt\" style=\"vertical-align:-3.42943pt\" version=\"1.1\" viewbox=\"-0.0498162 -5.96091 13.2759 9.39034\" width=\"13.2759pt\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\"><g transform=\"matrix(.013,0,0,-0.013,0,0)\"></path></g><g transform=\"matrix(.0091,0,0,-0.0091,6.097,3.132)\"><use xlink:href=\"#g50-87\"></use></g></svg>,</span> and spectral index <svg height=\"9.25202pt\" style=\"vertical-align:-3.29111pt\" version=\"1.1\" viewbox=\"-0.0498162 -5.96091 10.5631 9.25202\" width=\"10.5631pt\" xmlns=\"http://www.w3.org/2000/svg\" xmlns:xlink=\"http://www.w3.org/1999/xlink\"><g transform=\"matrix(.013,0,0,-0.013,0,0)\"></path></g><g transform=\"matrix(.0091,0,0,-0.0091,6.461,3.132)\"></path></g></svg> which carry significant information, we show that they impact the inflationary universe considerably. The tensor-to-scalar ratio concerning the curvature perturbation is worked out for the potential under consideration which is another significant observable and comes out to be nonnegative. In multifield models of inflation, both types of curvature and isocurvature perturbations exist, while, in the present work, during the slow-roll, isocurvature perturbations are suppressed and therefore can be neglected. The surviving perturbations which are due to the curvature only can be tackled suitably by a mechanism developed by Sasaki and Stewart known as Sasaki–Stewart formalism. The effect of augmenting the number of e-folds on the power spectrum through the spectral index and its impact on the observable parameters of the slow-roll inflationary phase is observed by carrying out the analysis. It is observed analytically that the spectrum of multifield inflation is effectively different than its corresponding single-field inflation. The field values and their masses affect the results profoundly at the time of horizon-crossing.","PeriodicalId":48962,"journal":{"name":"Advances in Astronomy","volume":"1 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2024-04-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140615567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Forecasting Ionospheric TEC Changes Associated with the December 2019 and June 2020 Solar Eclipses: A Comparative Analysis of OKSM, FFNN, and DeepAR Models","authors":"R. Mukesh, Sarat C. Dass, Negash Lemma Gurmu, M. Vijay, S. Kiruthiga, S. Mythili, D. Venkata Ratnam, V. B. S. Srilatha Indira Dutt","doi":"10.1155/2024/8255782","DOIUrl":"https://doi.org/10.1155/2024/8255782","url":null,"abstract":"This paper presents forecast and investigation of the variation in ionospheric Total Electron Content (TEC) during the solar eclipses (SEs) of December 2019 and June 2020 using three different methods: Deep Autoregressive model (DeepAR), Feed-Forward Neural Network (FFNN), and Ordinary Kriging-based Surrogate Model (OKSM), and the TEC data predicted by DeepAR, FFNN, and OKSM were compared with the actual TEC during the observation days. The study was conducted based on GPS data taken from the IISC receiver located in Bangalore, India, during the SEs which happened on 26.12.2019 and 21.06.2020. The TEC data were examined to assess the effect of solar eclipses on TEC values. Eighty-day prior TEC data for the IISC station are gathered from IONOLAB servers along with the other parameter data like Dst, Ap, F10.7, and Kp taken from OMNIWEB servers which were used to predict TEC. The reliability of the forecasted results is evaluated using numerical factors like Normalized Root Mean Square Error (NRMSE), Correlation Coefficient (CC), Root Mean Square Error (RMSE), Mean Absolute Error (MAE), and R-squared. The study demonstrates the usefulness of combining multiple methods for analyzing TEC variations during SEs and highlights the potential of OKSM, FFNN, and DeepAR models for studying TEC variation in the same context. The findings may be useful for satellite broadcasting and navigational services and for further research into the influence of solar eclipses on the TEC changes.","PeriodicalId":48962,"journal":{"name":"Advances in Astronomy","volume":"12 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2024-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140167382","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Measuring Track-Related Pointing Errors on the Nanshan Radio Telescope with an Optical Pointing Telescope","authors":"Ye Yuan, Zhi-Yong Liu, Na Wang","doi":"10.1155/2024/1538293","DOIUrl":"https://doi.org/10.1155/2024/1538293","url":null,"abstract":"The need for precise radio telescope pointing has driven great attention to investigating the effect of antenna local deformation or irregularity, such as unevenness in the azimuth track. Although the track-alidade interaction model is commonly used to investigate the pointing effect of track unevenness (such as the works on DSN 34 m antennas and the Green Bank Telescope), few experiments have been done to test the effectiveness of this model independently from the overall pointing model. To address this issue, a method utilizing an optical pointing telescope (OPT) for determining the impact of track unevenness on pointing is proposed. This method uses a group of reference pointing data collected by an OPT mounted at the bottom of the antenna alidade to extract the twist effect of the alidade from the radio telescope pointing data, thus compared with the predicted twist by the track-alidade model. This method was applied to the 26 meter Nanshan Radio Telescope (NSRT 26 m), achieving good agreement with the model-predicted values.","PeriodicalId":48962,"journal":{"name":"Advances in Astronomy","volume":"24 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2024-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140128073","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tracking and Disturbance Suppression of the Radio Telescope Servo System Based on the Equivalent-Input-Disturbance Approach","authors":"Lei Yang, Na Wang, Zhiyong Liu, Ning Li","doi":"10.1155/2024/5786292","DOIUrl":"https://doi.org/10.1155/2024/5786292","url":null,"abstract":"This paper presents a composite control algorithm for the radio telescope servo control system to address the target tracking and matched/mismatched disturbance suppression problems. The algorithm consists of the equivalent-input-disturbance (EID) approach and the optimal control method. An EID estimator is developed using the difference between the estimated output of the state observer and the measurement output and then the estimate of the EID is fed forward into the control input to reject the disturbance. A cost function with clear physical meaning is selected and the weighting parameters are adjusted for the optimal controller to improve tracking performance. Considering the nonminimum phase characteristics of the radio telescope system, the state observer gain is computed using the linear matrix inequality (LMI) method. The system stability is analyzed using the small gain theorem, and the linear quadratic regulator (LQR) control method is utilized to determine the state feedback gain. Finally, the composite controller is designed for an identified telescope model. Simulation results show that for the tracking performance, the settling time of proposed method is 1.13 s and reduces by about 0.32 s and 0.87 s than that of the ADRC controller and PI controller, respectively. For the antidisturbance performance, the RMS value and the maximum error of the proposed method are 0.0039 and 0.0128, which are 42.86% and 40.38% of the ADRC controller and 30.71% and 27.77% of the PI controller, respectively, which indicates that the proposed method has better control performance. In addition, the proposed controller has certain robustness to systematic parameter perturbations.","PeriodicalId":48962,"journal":{"name":"Advances in Astronomy","volume":"10 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2024-03-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140076110","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dark Energy from Cosmological Energy Conservation","authors":"Manuel Uruena Palomo","doi":"10.1155/2023/2882534","DOIUrl":"https://doi.org/10.1155/2023/2882534","url":null,"abstract":"The value of the gravitational wave energy density is unknown. Current progress in gravitational wave detection suggests that the energy density of the stochastic gravitational wave background (SGWB) will be estimated in the next decades. A derivation of its value is presented under the assumption that energy lost due to cosmic redshift is fully responsible for the energy gained by the cosmological constant in the expanding universe. This unknown nonlocal mechanism of energy conservation on the cosmic scale could explain dark energy and hint at a property of a theory of quantum gravity.","PeriodicalId":48962,"journal":{"name":"Advances in Astronomy","volume":"26 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136234249","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Predictions of Noncollinear Equilibria Positions in ER3BP with Yukawa-Like Corrections","authors":"E. B. Anitha, Tenaw Tilahun Asmamaw, M. J. Idrisi","doi":"10.1155/2023/7118712","DOIUrl":"https://doi.org/10.1155/2023/7118712","url":null,"abstract":"The existence and stability of noncollinear equilibrium points in the elliptic restricted three-body problem under the consideration of Yukawa correction to Newtonian potential are studied in this paper. The effects of various parameters (μ, ê, α, and λ) on the noncollinear equilibrium points are discussed briefly, and it is found that only ordinate of noncollinear equilibria E4,5 is affected by Yukawa correction while abscissa is affected by only mass parameter μ. The noncollinear equilibria was found linearly stable for a critical mass parameter μc. A critical point λ = ½ is also obtained for the critical mass parameter μc, and at this point, the critical mass parameter μc has maximum or minimum values according to α < 0 or α > 0, respectively.","PeriodicalId":48962,"journal":{"name":"Advances in Astronomy","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43058682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A New Approach to Astronomical Data Analysis Based on Multiple Variables","authors":"Prasenjit Banerjee, A. Chattopadhyay, Soumita Modak","doi":"10.1155/2023/8682054","DOIUrl":"https://doi.org/10.1155/2023/8682054","url":null,"abstract":"Data analysis for a sample of celestial bodies generally is preceded by the completeness test in order to verify whether the sample objects are proper representatives of the corresponding part of the universe. A data set following a multivariate, continuous, uniform distribution is said to be “complete in space.” This paper introduces a new approach to check for this completeness for any astronomical data set under a multivariate setup. Our proposed procedure, using the multiple tests of hypotheses based on nonparametric statistics, and consequently, combining their \u0000 \u0000 p\u0000 \u0000 values, outperforms others from the literature.","PeriodicalId":48962,"journal":{"name":"Advances in Astronomy","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48546695","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Propagation of Nonlinear Dust-Acoustic Waves in a Self-Gravitating Collision Magnetized Dusty Plasma in Earth’s Magnetosphere","authors":"A. Almuqrin, M. Alotiby, R. Tolba","doi":"10.1155/2023/4548171","DOIUrl":"https://doi.org/10.1155/2023/4548171","url":null,"abstract":"The nonlinear propagation of different types of DANW acoustic dust nonlinear waves has been investigated in a magnetized dusty plasma consisting of negatively charged dust particles, Maxwellian electrons, and ions. Application of the standard reductive perturbation theory is used to derive the corresponding three-dimensional nonlinear a complex Ginzburg–Landau (3D-CGLE) equation which governs the dynamics of the dust-acoustic wave packets. The stationary analytical solutions of the CGLE are numerically analysed where the effect of the physical parameters of the dusty plasma model on the wave’s propagation is taken into account. It has been found that there can be a relationship between the appearance of soliton waves and electromagnetic waves, as well as between shock-like waves and periodic travelling waves. Expression of the importance of these findings is the cornerstone of explaining the true relationship between the propagation of nonlinear waves in the physics of space, for example, the Earth’s magnetic field.","PeriodicalId":48962,"journal":{"name":"Advances in Astronomy","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-06-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45116173","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Noncollinear Equilibrium Points in CRTBP with Yukawa-Like Corrections to Newtonian Potential under an Oblate Primary Model","authors":"M. J. Idrisi, Sunusi Haruna, Teklehaimanot Eshetie","doi":"10.1155/2023/4932794","DOIUrl":"https://doi.org/10.1155/2023/4932794","url":null,"abstract":"This study is about the effects of Yukawa-like corrections to Newtonian potential on the existence and stability of noncollinear equilibrium points in a circular restricted three-body problem when bigger primary is an oblate spheroid. It is observed that ∂x0/∂λ = 0 = ∂y0/∂λ at λ0 = 1/2, so we have a critical point λ0 = 1/2 at which the maximum and minimum values of x0 and y0 can be obtained, where λ ∈ (0, ∞) is the range of Yukawa force and (x0, y0) are the coordinates of noncollinear equilibrium points. It is found that x0 and y0 are increasing functions in λ in the interval 0 < λ < λ0 and decreasing functions in λ in the interval λ0 < λ < ∞ for all α ∈ α+. On the other hand, x0 and y0 are decreasing functions in λ in the interval 0 < λ < λ0 and increasing functions in λ in the interval λ0 < λ < ∞ for all α ∈ α−, where α ∈ (−1, 1) is the coupling constant of Yukawa force to gravitational force. The noncollinear equilibrium points are found linearly stable for the critical mass parameter β0, and it is noticed that ∂β0/∂λ = 0 at \u0000 \u0000 \u0000 \u0000 λ\u0000 \u0000 ∗\u0000 \u0000 \u0000  = 1/3; thus, we got another critical point which gives the maximum and minimum values of β0. Also, ∂β0/∂λ > 0 if 0 < λ < \u0000 \u0000 \u0000 \u0000 λ\u0000 \u0000 ∗\u0000 \u0000 \u0000 and ∂β0/∂λ < 0 if \u0000 \u0000 \u0000 \u0000 λ\u0000 \u0000 ∗\u0000 \u0000 \u0000  < λ < ∞ for all α ∈ α−, and ∂β0/∂λ < 0 if 0 < λ < \u0000 \u0000 \u0000 \u0000 λ\u0000 \u0000 ∗\u0000 \u0000 \u0000 and ∂β0/∂λ > 0 if \u0000 \u0000 \u0000 \u0000 λ\u0000 \u0000 ∗\u0000 \u0000 \u0000  < λ < ∞ for all α ∈ α+. Thus, the local minima for β0 in the interval 0 < λ < \u0000 \u0000 \u0000 \u0000 λ\u0000 \u0000 ∗\u0000 \u0000 \u0000 can also be obtained.","PeriodicalId":48962,"journal":{"name":"Advances in Astronomy","volume":" ","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43925742","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Thermal Modeling of Oxia Planum: Thermophysical Characterization of the Dark Resistant Unit (DRU) in the Germania Lacus","authors":"M. Formisano, F. Altieri, A. Frigeri, M. D. De Sanctis, C. Federico, G. Magni, E. Ammannito, S. De Angelis, M. Ferrari","doi":"10.1155/2023/8869504","DOIUrl":"https://doi.org/10.1155/2023/8869504","url":null,"abstract":"The aim of this work is to characterize, from a thermophysical perspective, the dark resistant unit (DRU) characterizing Germania Lacus in the Oxia Planum Region, providing new insights to constrain the nature of the materials which compose this unit. We investigated the temperature distribution of the DRU by adopting common values of the thermophysical parameters of the basalt and by exploring several values of porosity. As an additional case, we also explore a composition made of pebbles. The numerical model developed here represents a follow-up of the work recently published by Formisano et al. 2021, and it takes into account a large-scale topography of the site and assumes a diurnal temperature profile for the atmosphere rather than a constant value (unlike Formisano et al. 2021). Comparisons with Mars Pathfinder and Viking data as well as numerical models are also reported. The methodology described here could be useful to characterize as well other sites on Mars’ surface with available small-scale topographic data.","PeriodicalId":48962,"journal":{"name":"Advances in Astronomy","volume":"1 1","pages":""},"PeriodicalIF":1.4,"publicationDate":"2023-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41749698","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}