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Research Article
4D Gravitational Collapse Spherically Symmetric Spacetime in f(R,T) Theory with Cosmological Constant
Issue:
Volume 13, Issue 4, August 2025
Pages:
74-90
Received:
27 April 2025
Accepted:
19 May 2025
Published:
23 July 2025
DOI:
10.11648/j.ajpa.20251304.12
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Views:
Abstract: This study explores the behavior of an anisotropic fluid in a spherically symmetric spacetime by examining expanding and collapsing solutions to the Einstein Field Equations (EFEs) within the framework of f(R,T) gravity. This modified theory of gravity extends General Relativity by allowing the gravitational action to depend on both the Ricci scalar R and the trace T of the energy-momentum tensor. The work incorporates a cosmological constant to assess its influence on the evolution of the fluid. A central aim of the study is to understand how the interaction between the Ricci scalar, the expansion scalar, and the trace of the energy-momentum tensor affects the dynamics of the system. Special attention is given to the anisotropic nature of the fluid, where radial and tangential pressures differ adding complexity to both expansion and collapse processes. The presence of a cosmological constant further modifies the pressure and density profiles, revealing how dark energy-like effects can shape the evolution of matter under gravity. The research identifies the existence of a single horizon in the system and uses a mass function to analyze the formation of trapped surfaces regions where outgoing light rays begin to converge, indicating gravitational collapse. Additionally, the relationship between the coupling constants Λ (cosmological constant) and λ (associated with the f(R,T) theory) is explored for both collapsing and expanding scenarios. Graphical results highlight the influence of these parameters on pressure, mass, anisotropy, and energy density, offering valuable insights into modified gravity’s role in astrophysical phenomena.
Abstract: This study explores the behavior of an anisotropic fluid in a spherically symmetric spacetime by examining expanding and collapsing solutions to the Einstein Field Equations (EFEs) within the framework of f(R,T) gravity. This modified theory of gravity extends General Relativity by allowing the gravitational action to depend on both the Ricci scala...
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Research Article
Hydrogeophysical Assessment and Protective Capacity of Groundwater Resources in Kingsley Ozumba Mbadiwe University Ideato and Environs, Southeastern Nigeria
Issue:
Volume 13, Issue 4, August 2025
Pages:
91-106
Received:
25 June 2025
Accepted:
7 July 2025
Published:
30 July 2025
Abstract: Geoelectrical investigations were carried out to determine the aquifer potentials and protective capacity of Kingsley Ozumba Mbadiwe University Ideato and environs, Imo State, Southeastern Nigeria. A total of twenty-five (25) Vertical Electrical Sounding survey was conducted using the Schlumberger array to evaluate the characteristics of the aquifers in the studied locations. Geoelectric sections derived from the modeling of the sounding data reveal 7 to 9 subsurface layers and characterized by four main sounding curve types-KH-type, HA-type, HK-type and KA-type. The study area is underlain by alternating layers of shale, sand/sandstone and clay. The aquifer is delineated within the sand/sandstone Formation. The aquifer resistivity ranges from 390 to 450000 Ωm, while the aquifer thickness and depth range from 4.7 to 168.6m and 6.5 to 109m respectively. The Dar Zarrouk parameters of longitudinal conductance ranges from 0.000227 to 0.12134 mhos, whereas the transverse resistance ranges from 1833 to 54223904Ωm2. The transmissivity in the study area has its highest value of 684.57 m2/day at Amaikpa Ogboko and its lowest value of 19.08m2/day at Ogume. Overall, the transmissivity of the study area indicates a relatively high to moderate ability of the aquifer to transmit water, with an exception of Ogume. Furthermore, the aquifer potentials of the study area were shown to differ with aquifer size, structure and characteristics and are influenced by the underlying geology generally. The study area has an overall poor aquifer protective capacity. This suggests that the aquifer is very susceptible to surface contaminants and the groundwater is at risk of pollution. Proper environmental and waste monitoring management is therefore strongly suggested in the study area to protect the groundwater resources.
Abstract: Geoelectrical investigations were carried out to determine the aquifer potentials and protective capacity of Kingsley Ozumba Mbadiwe University Ideato and environs, Imo State, Southeastern Nigeria. A total of twenty-five (25) Vertical Electrical Sounding survey was conducted using the Schlumberger array to evaluate the characteristics of the aquife...
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Review Article
Variation of Phonons Self-energy - Frequency and Linewidth - of Permanent Phonons in YBCO/LCMO Superlattices Thin Films Due to the Change of Temperature Using Raman Light Scattering
Nadir Driza*
,
Asma Rajab Salem Elgade
Issue:
Volume 13, Issue 4, August 2025
Pages:
107-114
Received:
29 May 2025
Accepted:
20 June 2025
Published:
12 August 2025
Abstract: In order to write this article, we looked at the impact of temperatures variation going from low to high temperature starting from 10 K to 300 K on my samples. The work was performed by using Raman light scattering which is a powerful technique to fulfill that aim perfectly on thin films of YBCO/LCMO superlatticse - with different thickness of both YBCO layers and LCMO layers -, bulk YBCO and bulk LCMO as seen in table 1. During this work, we focus our study on the permanent phonons of YBCO/LCMO as a thin film, which were 240 cm-1, 340 cm-1, 440 cm-1 and 505 cm-1 phonon modes. Depending on our data, which we obtained from experiment’s measurement we could confirm that the variation of temperature gives rise to change in frequency and linewidth in all phonons were observed during this study. Therefore, we could conclude that the all phonons studied in this article collapse depending on the increasing of the temperature in the form of suppression of phonons self-energy in the form of softening and hardening, but with different degrees. Because of that, we clearly observed expected and unexpected behaviour of frequency and linewidth of all permanent phonons of YBCO/LCMO thin films - where we partially builded up our work on this observation in this article - at TC and TCurie, respectively.
Abstract: In order to write this article, we looked at the impact of temperatures variation going from low to high temperature starting from 10 K to 300 K on my samples. The work was performed by using Raman light scattering which is a powerful technique to fulfill that aim perfectly on thin films of YBCO/LCMO superlatticse - with different thickness of both...
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