In this paper we study a modified version of unimodular general relativity in the context of f (G), G denoting the Gauss-Bonnet invariant. We focus on Bianchi-type I and Friendmann-Robertson-Walker universes and search for unimodular f (G) models according to the de Sitter and power-law solutions. Assuming unimodular f (G) gravity as a perfect fluid and making use of the slow-roll parameters, the inflationary model has been reconstructed in concordance with the Planck observational data. Moreover, we investigate the realization of the bounce and loop quantum cosmological ekpyrotic paradigms. Assuming suitable and appropriate scale factors, unimodular f (G) models able to reproduce superbounce and ekpyrotic scenarios have been reconstructed.

The chaotic behavior of the modified Rayleigh-Duffing oscillator with φ 6 potential and external excitation is investigated both analytically and numerically. The so-called oscillator models, for example, ship rolling motions. The single well and triple well potential cases are considered. Melnikov method is applied and the conditions for the existence of homoclinic and heteroclinic chaos are obtained. The effects of nonlinear damping on roll motion of ships are analyzed in detail. As it is known, nonlinear roll damping is a very important parameter in estimating ship responses. It is noted that the pure and unpure quadratic damping parameters affect the Melnikov criterion in the heteroclinic and homoclinic cases respectively while the pure cubic parameter affects the amplitude in both cases. The predictions have been tested with numerical simulations based on the basin of attraction. It is pointed out that certain quadratic damping effects are contrary to cubic damping effect.

We investigate in this paper the structures of neutron stars under the strong magnetic field in the framework of f (T ) gravity where T denotes the scalar torsion. The TOV equations in this theory of gravity have been considered and numerical resolution of these equations has been performed within perturbative approach taking into account the equation of state of neutron dense matter in magnetic field. We simplify the problem by considering the very strong magnetic field which affects considerably the dense matter; and for quadratic and cubic corrections to Teleparallel term, one finds that the mass of neutron stars can increase for different values of the perturbation parameter. The deviation from Teleparallel for different values of magnetic field is found out and this feature is very appreciable in the case of cubic correction. Our results are related to the hadronic particles description with very small hyperon contributions and the mass-radius evolution is consistency with the observational data.

In this paper, the Helmholtz equation with quadratic damping themes is used for modeling the dynamics of a simple prey-predator system also called a simple Lotka–Volterra system. From the Helmholtz equation with quadratic damping themes obtained after modeling, the equilibrium points have been found, and their stability has been analyzed. Subsequently, the harmonic oscillations have been studied by the harmonic balance method, and the phenomena of resonance and hysteresis are observed. The primary and secondary resonances have been researched by the multiple-scale method, and the conditions of stability of the amplitudes of oscillations are determined. Chaos is detected analytically by the Melnikov method and numerically using the basin of attraction, the bifurcation diagram, the Lyapunov exponent, the phase portrait, and the Poincaré section. The effects of all the parameters of the system are analyzed in detail, and special emphasis is placed on the new parameters. Through this analysis, the complex phenomena such as hysteresis, bistability, amplitude jump, resonances, and chaos have been obtained. The control of the parameters and the necessary conditions to control the aforementioned phenomena have been found.