Role of f(G) Gravity in the Study of Non-Static Complex Systems

The concept of complexity for dynamical spherically symmetric dissipative self-gravitating configuration [1] is generalized in the scenario of modified Gauss-Bonnet gravity. For this purpose, a spherically symmetric fluid with locally anisotropic, dissipative, and non-dissipative configuration is considered. We choose the same complexity factor for the structure as we did for the static case, while we consider the homologous condition for the simplest pattern of evolution. In this approach, we formulate structure scalars that demonstrate the essential properties of the system. A fluid distribution that fulfills the vanishing complexity constraint and proceeds homologously corresponds to isotropic, geodesic, homogeneous, and shear-free fluid. In the dissipative case, the fluid is still geodesic but it is shearing, and there is a wide range of solutions. In the last, the stability of vanishing complexity is examined.

Vessel tree extraction using radius-lifted keypoints searching scheme and anisotropic fast marching method

Geodesic methods have been widely applied to image analysis. They are particularly efficient to extract a tubular structure, such as a blood vessel, given its two endpoints in a 2D or 3D medical image. We address here a more difficult problem: the extraction of a full vessel tree structure given a single initial root point, by growing a collection of keypoints or new initial source points, connected by minimal geodesic paths. In this article, those keypoints are iteratively added, using a new detection criteria, which utilize the weighted geodesic distances with respect to a radius-lifted Riemannian metric, the standard Euclidean curve length and a path score. Two main weaknesses of classical keypoints searching approach are that the weighted geodesic distance and the Euclidean path length do not take into account the orientation of the tubular structure or object boundaries, due to the use of an isotropic geodesic Riemannian metric, and suffer from a leakage problem. In contrast, we use an anisotropic geodesic Riemannian metric, and develop new criteria for selecting keypoints based on the path score and automatically stopping the tree growth. Experimental results demonstrate that our method can obtain the expected results, which can extract vessel structures at a finer scale, with increased accuracy.

Sp(4, R)/GL(2, R) Matrix Structure of Geodesic Solutions for Einstein–Maxwell–Dilaton–Axion Theory

The Sp (4, R)/ GL (2, R) matrix operator defining the family of isotropic geodesic lines in the target space of the stationary D = 4 Einstein–Maxwell–dilaton–axion theory is constructed. This operator is used to derive a class of solutions describing a system of point centers with nontrivial values of mass, parameter NUT, as well as electric, magnetic, dilaton and axion charges. It is shown that this class contains the Majumdar–Papapetrou-like solutions and also the solutions for massless naked singularities.

ELECTROMAGNETIC RADIATION INDUCED BY A GRAVITATIONAL WAVE

Conversion of a gravitational wave into an electromagnetic one in a laser coherent emission field is studied. As a result two electromagnetic waves are created. For calculation the Maxwell equations in three-dimensional vector form are used. Optimal detection of the gravitational wave is discussed. In a particular case it is the laser interferometric antenna. This approach is identical to those based on integration of the isotropic geodesic equation, the eikonal equation, giving the three-pulsing response of the electromagnetic signal obtained by Estabrook and Wahlquist. It also results in the matrix method developed by Vinet for calculation of laser interferometric antennae.

Relativistic Reduction of Astrometric Observations at Points Level of Accuracy

The framework of general relativity theory (GRT) is applied to the problem of reduction of high precision astrometric observations of the order of one microarcsecond. The equations of geometric optics for the non-stationary gravitational field of the Solar system have been deduced. Integration of the equations of geometric optics results in the isotropic geodesic line connecting the source of emission (a star, a quasar) and an observer. This permits to calculate the effects of relativistic aberration of light due to monopole and quadrupole components of the gravitational field of the Sun and the planets taking into account their motions and rotation. Transformations between the reference systems are used to calculate the light aberration occurring when passing from the satellite system to the geocentric system and from the geocentric system to the baryecntric system. The baryecntric components of the observed position vector reduced to the flat space-time are corrected, if necessary, for parallax and proper motion of a celestial object using the classical techniques of Euclidean geometry.