Exact Solutions For Einstein-Rosen Universe

Iordana Astefanoaei, Gheorghe Maftei
Department of Theoretical Physics, "Al.I. Cuza" University,
Bd. Copou 11, RO-6600 Iasi, Romania
E-mail: iordana@uaic.ro

Abstract. In this paper we analyse the behaviour of the background gravitational radiation in the aproximation of the far matter fields in a cosmological model based on the Einstein-Rosen solution. Because the properties of the gravitational waves obtained as the solutions of Einstein fields equations ( the gravitational field equations) are the most obvious in the weak gravitational fields, we consider here that the matter source is not specified. Using the Newman-Penrose formalism, we calculate in a null-tetradic base the spin coefficients, the directional derivatives, and the tetradic components of Ricci and Weyl tensors.
The vacuum space-time solution and the energetic conditions lead us to the solution for(z,t) which defines the gravitational waves. The function p(z,t) describes the transverse part of the gravitational wave which propagates in an Universe with algebraic classification of the Petrov type N (radiative universe). Only in the particular case when t tends to infinity, p(z,t) leads to the primordial gravitational waves which were not included here.

Key words: gravitational wave - Einstein-Rosen solution - Newman-Penrose formalism -energy-momentum pseudo-tensor - gravitational field.
 
 

Une Metrique Riemannienne Dans L'Espace Des Phases D'Un Systeme Dynamique Conservatif

Mihail Barbosu
Universite "Babes-Bolyai", Faculte de Mathematiques et Informatique
1, rue Kogalniceanu, RO-34003400 Cluj-Napoca, Roumanie
E-mail: mbarbosu@math.ubbcluj.ro

Resume. Dans ce travail on propose une metrique adaptee a l'espace des phases d'un systeme dynamique. Cette metrique est baseee sur la metrique de Sasaki et permet d'amorcer des etudes qualitatives des geodesiques, qui sont dans ce cas les trajectoires de l'espace des phases. Afin de preparer des etudes geometriques ulterieures, nous avons donne explicitement les composantes du tenseur metrique fondamental dans le problème de Kepler et dans le problème plan des trois corps.

Mots cles: mecanique celeste - probleme plan des trois corps - geometrie riemannienne.
 
 
 

The Two-Body Problem In The Point Mass Approximation Field. I. Collision And Near-Collision Dynamics

Vasile Mioc, Magda Stavinschi
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212 Bucharest, Romania
E-mail: vmioc@roastro.astro.ro, magda@roastro.astro.ro

Abstract. Newton's theorem about the point mass approximation is fully correct only in fields with potentials of the form A/r + Br^2. Here r is the distance between particles, and A, B are real parameters. A systematic qualitative study of the two-body problem in such a field is being started here. The equations of motion are written in Hamiltonian formalism, and the first integrals of energy and angular momentum are pointed out. Using McGehee's transformations, the motion equations are regularized, and the collision singularity is replaced by the collision manifold. The flow on this manifold and in its neighbourhood is depicted.

Key words: celestial mechanics - two-body problem -qualitative analysis - McGehee's transformations.
 
 

The Two-Body Problem In The Point Mass Approximation Field. II. Escape and Near-Escape Dynamics

Vasile Mioc, Magda Stavinschi
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212 Bucharest, Romania
E-mail: vmioc@roastro.astro.ro, magda@roastro.astro.ro

Abstract. The study of the two-body problem in the point mass approximation field (featured by the potential A/r + Br^2, with r = distance between particles, and A, B = real nonzero constants) is continued by tackling the situation r tends to infinity. The infinity singularity is blown up via McGee-type transformations, and the infinity manifold is pasted on the phase space. The fictitious flow on this manifold is described, and the local flow near infinity, too.

Key words: celestial mechanics - two-body problem - qualitative analysis - McGehee transformations.
 
 
 
 

The Two-Body Problem In The Point Mass Approximation Field.III. Equilibria

Vasile Mioc, Magda Stavinschi
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212 Bucharest, Romania
E-mail: vmioc@roastro.astro.ro, magda@roastro.astro.ro

Abstract. One continues the study of the two-body problem in the point mass approximation field (characterized by a force function A/r + Br^2, with r = distance between particles, and A,B = real nonzero constants) by searching for equilibria. Various types of fixed points are found for the whole interplay among field parameters, angular momentum, and energy level. The only unstable relative equlibirum indicates the possible existence of a homoclinic loop.

Key words: celestial mechanics - two-body problem - qualitative analysis - equilibria
 
 

CCD Observations Of Galilean Satellites' Mutual Phenomena, Made In Bucharest, During PHEMU '97 Campaign. I. Observations With High Accuracy Timing; Eclipses

Gheorghe Vass
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212, Bucharest, Romania
E-mail: gvass@roastro.astro.ro

Abstract. The paper presents some CCD observations of Galilean satellites' mutual phenomena, made in Bucharest, during PHEMU '97 observational campaign. There are included only the light curves of the mutual eclipses that were obtained on the base of Gaussian fitting of the starlike objects.

Key words: mutual phenomena - CCD observations - Galilean satellites' eclipses
 
 

CCD Observations Of Galilean Satellites' Mutual Phenomena, Made in Bucharest, During PHEMU '97 Campaign.II. Observations With High Accuracy Timing; Occultations

Gheorghe Vass, Liviu Serbanescu
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212, Bucharest, Romania
E-mail: gvass@roastro.astro.ro, livius@roastro.astro.ro

Abstract. The paper presents some CCD observations of Galilean satellites' mutual phenomena, made in Bucharest, during PHEMU'97 observational campaign. There are included only the light curves of the mutual phenomena that were not obtained on the base of Gaussian fitting of the measured objects; it is the case of the observed occultations.

Key words: mutual phenomena - CCD observations - Galilean satellites' occultations
 
 

CCD Observations Of Galilean Satellites' Mutual Phenomena, Made in Bucharest, During PHEMU'97 Campaign.III. Observations Without High Accuracy Timing

Alexandru Dumitrescu (1), Gabriel Stefanescu (1), Stefan Sorescu (2)
(1) Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212, Bucharest, Romania
E-mail: alex@roastro.astro.ro
(2) Bucharest University, Faculty of Physics (Student)

Abstract. The paper presents observations of the mutual phenomena of the Galilean satellites made in Bucharest, using a CCD camera attached on a Cassegrain Telescope, during the PHEMU'97 campaign. The light curves were obtained on base of Gaussian fitting of the starlike objects.

Key words: Galilean satellites - mutual phenomena - CCD observations
 
 

A Selection Of Solar Eclipses Recorded In Old Romanian Chronicles And Notes

Magda Stavinschi (1), Vasile Mioc (1), Suzanne Debarbat (2)
(1) Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212 Bucharest, Romania
E-mail: magda@roastro.astro.ro, vmioc@roastro.astro.ro
(2) Observatoire de Paris, DANOF
61, Avenue de l'Observatoire, F-75014 Paris, France

Abstract. Some solar eclipses recorded in Romanian chronicles and notes on old books and manuscripts are surveyed.

Key words: history of astronomy - solar eclipses.
 
 

Solar Eclipses In Romania (1801 - 2010)

Nedelia Popescu, Erasmia Coporan, Marian Doru Suran
Astronomical Institute of the Romanian Academy
Str. Cutitul de Argint 5, RO-75212, Bucharest 28, Romania
E-mail: delia@roastro.astro.ro, suran@roastro.astro.ro

Abstract: Some data concerning the solar eclipses occured in Romania in the interval 1801 - 2010 are presented.

Key words: solar eclipses in Romania - solar eclipses circumstances