H. Rodrigues

DELTA MATTER FORMATION IN DENSE ASYMMETRIC NUCLEAR MEDIUM

In the context of a relativistic mean field theory the delta-resonance matter formation in a highly compressed nuclear medium is investigated. For a given set of nucleon–meson coupling constants, the delta-resonance formation is studied by changing the delta-meson coupling constants. The effect on the equation of state and on the delta-resonance population with respect to changes in the delta-resonance coupling constants values is discussed for very asymmetric and quasi-symmetric nuclear matter, as an extension of works restricted to the symmetric nuclear matter treatment.5,6

EFFECTS OF Δ-BARYON INTERACTION STRENGTH ON NEUTRON STARS PROPERTIES

We investigate the effect of Δ-resonance interaction strength on the equation of state of asymmetric hadronic matter and neutron stars structure. We discuss Δ-matter formation at high densities in the context of a relativistic mean field theory. We show that the attractive nature of the Δ-baryon interaction can induce a phase transition accompanying Δ-matter formation, at values of densities presumably existing in central regions of neutron stars. The possibility of a rich Δ-resonance neutron star is presented using the proposed equation of state.

Perfect transfer of quantum states in a network of harmonic oscillators

This work presents an exactly soluble scheme to address the problem of optimal transfer of quantum states through a set of s harmonic oscillators composing a network with connected ends as a closed quantum circuit. For this purpose we start from a general quadratic Hamiltonian form. The relationship between the parameters of the Hamiltonian, the network size, and the time interval required for such transfer are explicitly shown. Particular physical realizations of this Hamiltonian, transfer of entangled states, including transfer of states at the expense of a quantum entanglement, are also considered.

Modeling compact stars without numerical integration

Taking a novel approach, this paper discusses the structure of compact stars, an important topic in theoretical astrophysics. Adopting Newtonian gravitation, we solve the hydrostatic equilibrium equation by imposing a simple parametrization for the mass density inside the star. The solutions of the equilibrium equation are carried out without numerical integration, with the aim of determining a few global properties of white dwarfs and neutron stars. The global properties of compact stars are thus provided by simple algebraic relationships. The model is intended as an introductory approach to the study of compact stars at an undergraduate or graduate level.

On determining the kinetic content of ellipsoidal configurations

Determining the velocity field of structures such as galaxies, stars, and fluid planets is a relevant topic in astrophysics and astronomy. Depending on the shape of the astrophysical object, the internal velocity field may be obtained by means of analytical methods. Specifically, ellipsoidal configurations are the most simple and natural generalization of spherically symmetric mass distributions, when rotation is present. In this work one obtains closed analytical expressions of the velocity field and of the kinetic energy of uniform ellipsoidal configurations composed of compressible fluids. With this aim, the equation of continuity is solved allowing a description of the irrotational velocity field within the system. This permits obtaining analytical expressions of the kinetic energy for each specific mass distribution.

Modeling the dynamics of single-bubble sonoluminescence

Sonoluminescence (SL) is the phenomenon in which acoustic energy is (partially) transformed into light. It may occur by means of one bubble or many bubbles of gas inside a liquid medium, giving rise to the terms single-bubble and multi-bubble sonoluminescence (SBSL and MBSL). In recent years some models have been proposed to explain this phenomenon, but there is still no complete theory for the light-emission mechanism (especially in the case of SBSL). In this paper, we do not address this more complicated specific issue, but only present a simple model describing the dynamical behavior of the sonoluminescent bubble in the SBSL case. Using simple numerical techniques within the Matlab software package, we discuss solutions that consider various possibilities for some of the parameters involved: liquid compressibility, surface tension, viscosity and type of gas. The model may be used for an introductory study of SL on undergraduate or graduate physics courses, and as a clarifying example of a physical system exhibiting large nonlinearity.

Modelling the dynamics of bodies self-propelled by exponential mass exhaustion

We present a study of the ascending vertical motion of a self-propelled body under a uniform gravitational field suffering the action of two different types of air friction forces: linear on the velocity, which is valid for slowly moving bodies, and quadratic on the velocity. We study the special case where the thrust force is a decreasing function of mass, which corresponds to the exponential mass exhaustion rate. We present in detail the analytical solutions for the equations of motion for the two types of air friction, and briefly present some techniques for solving the related ordinary differential equations. This paper is intended for undergraduate physics teachers and for graduate students.

Modelling the motion of meteors in the Earth's atmosphere

This work discusses the motion of meteors in the Earths atmosphere. The equations of motion of the projectile are presented and a simplified numerical approach to solve them is discussed. An algorithm for solving the equations of motion is constructed, and implemented in a very simple way using Excel software. The paper is intended as an example of the application of Newtons laws of motion at undergraduate level.

Delta Resonance Coupling with Walecka’s Mesons: Implications to Stellar Matter EoS

In this work we have obtained the equation of state to the highly asymmetric dense stellar matter, using the nonlinear Walecka model in the mean field approximation. We discussed the implication of changes in coupling constant of the delta baryonic resonance on the observable of the neutron star. A detailed analysis of the equation of state and of the baryonic effective mass in respect to changes in the delta coupling constants is carried out. We focus attention on a new aspect observed for pressure when varying the baryonic density of the medium; a first order phase transition like a liquid-gas phase transition was observed for an acceptable range of delta coupled constant values. We have explored the implication of this aspect for the neutron star structure and their maximum masses.

Shock wave produced by hadron-quark phase transition in neutron star

In this work we present a schematic description of the detonation wave in hadronic matter inside a neutron star core. We have used a simplified two shells model where the inner shell medium is initially composed of a small lump of strange quark matter surrounded by a large outer shell composed of hadronic matter. We have utilized an equation of state (EOS) based on Relativistic Mean Field Theory with the parameter set NL3 to describe the nuclear and subnuclear phases. We use the MIT bag model to describe the strange quark matter. The hadron-quark phase transition actually induces highly non equilibrium modes, which may become a detonation process (faster) or a burning process (slower). The main purpose of the work is to study the formation of a remnant quark star and the possibility of mass ejection caused by the hadron-quark phase transition. We have found that the total amount of ejected mass is dependant of the bag constant utilized in the strange matter description.