Faithful transformation of quasi-isotropic to Weyl-Papapetrou coordinates: A prerequisite to compare metrics

We demonstrate how one should transform correctly quasi-isotropic coordinates to Weyl-Papapetrou coordinates in order to compare the metric around a rotating star that has been constructed numerically in the former coordinates with an axially symmetric stationary metric that is given through an analytical form in the latter coordinates. Since a stationary metric associated with an isolated object that is built numerically partly refers to a non-vacuum solution (interior of the star) the transformation of its coordinates to Weyl-Papapetrou coordinates, which are usually used to describe vacuum axisymmetric and stationary solutions of Einstein equations, is not straightforward in the non-vacuum region. If this point is \textit{not} taken into consideration, one may end up to erroneous conclusions about how well a specific analytical metric matches the metric around the star, due to fallacious coordinate transformations.Comment: 18 pages, 2 figure

Nodal and Periastron Precession of Inclined Orbits in the Field of a Rapidly Rotating Neutron Star

We derive a formula for the nodal precession frequency and the Keplerian period of a particle at an arbitrarily inclined orbit (with a minimum latitudinal angle reached at the orbit) in the post-Newtonian approximation in the external field of an oblate rotating neutron star (NS). We also derive formulas for the nodal precession and periastron rotation frequencies of slightly inclined low-eccentricity orbits in the field of a rapidly rotating NS in the form of asymptotic expansions whose first terms are given by the Okazaki--Kato formulas. The NS gravitational field is described by the exact solution of the Einstein equation that includes the NS quadrupole moment induced by rapid rotation. Convenient asymptotic formulas are given for the metric coefficients of the corresponding space-time in the form of Kerr metric perturbations in Boyer--Lindquist coordinates.Comment: 12 page

The influence of the Lande gg-factor in the classical general relativistic description of atomic and subatomic systems

We study the electromagnetic and gravitational fields of the proton and electron in terms of the Einstenian gravity via the introduction of an arbitrary Lande $g$-factor in the Kerr-Newman solution. We show that at length scales of the order of the reduced Compton wavelength, corrections from different values of the $g$-factor are not negligible and discuss the presence of general relativistic effects in highly ionized heavy atoms. On the other hand, since at the Compton-wavelength scale the gravitational field becomes spin dominated rather than mass dominated, we also point out the necessity of including angular momentum as a source of corrections to Newtonian gravity in the quantum description of gravity at this scale.Comment: 11 pages, 2 figure

Singular sources in the Demianski-Newman spacetimes

The analysis of singular regions in the NUT solutions carried out in the recent paper (Manko and Ruiz, 2005 Class. Quantum Grav. 22, p.3555) is now extended to the Demianski-Newman vacuum and electrovacuum spacetimes. We show that the effect which produces the NUT parameter in a more general situation remains essentially the same as in the purely NUT solutions: it introduces the semi-infinite singularities of infinite angular momenta and positive or negative masses depending on the interrelations between the parameters; the presence of the electromagnetic field additionally endows the singularities with electric and magnetic charges. The exact formulae describing the mass, charges and angular momentum distributions in the Demianski-Newman solutions are obtained and concise general expressions P_n=(m+i\nu)(ia)^n, Q_n=(q+ib)(ia)^n for the entire set of the respective Beig-Simon multipole moments are derived. These moments correspond to a unique choice of the integration constant in the expression of the metric function \omega which is different from the original choice made by Demianski and Newman.Comment: 22 pages, 5 figures; submitted to Classical and Quantum Gravit

Hyperfibrinogenemia and Increased Stiffness of Plasma Clots in the Active Systemic Lupus Erythematosus

© 2017, Springer Science+Business Media, LLC. Systemic lupus erythematosus (SLE) is an autoimmune disease associated with an increased risk of thrombosis. We hypothesized that inflammation-associated hyperfibrinogenemia can contribute to the prothrombotic phenotype of fibrin clots by changing their mechanical properties. Twenty-eight SLE patients were categorized based on their disease activity scores (SLEDAI) into the groups with inactive (SLEDAI   4, n = 14) forms of the disease. Clots from individual platelet-free plasma samples were probed using shear rheometry and viscoelastic properties of the fibrin gels were determined as the storage (G′) and loss (G″) moduli. A significant increase of G′ was revealed in the clots from the plasma of active SLE patients over inactive SLE, which correlated with elevated fibrinogen levels. Clots from the plasma of inactive SLE patients had the elasticity and fibrinogen levels indistinguishable from those in control plasma from healthy subjects. Thus, inflammatory hyperfibrinogenemia in the active SLE form makes fibrin clots stiffer which has been previously shown to be associated with a higher incidence of thrombotic disorders

The rotation curve and mass-distribution in highly flattened galaxies

A new method is developed which permits the reconstruction of the surface-density distribution in the galactic disk of finite radius from an arbitrary smooth distribution of the angular velocity via two simple quadratures. The existence of upper limits for disk's mass and radius during the analytic continuation of rotation curves into the hidden (non-radiating) part of the disk is demonstrated.Comment: 13 pages, 2 figure

Electric force lines of the double Reissner-Nordstrom exact solution

Recently, Alekseev and Belinski have presented a new exact solution of the Einstein-Maxwell equations which describes two Reissner-Nordstrom (RN) sources in reciprocal equilibrium (no struts nor strings); one source is a naked singularity, the other is a black hole: this is the only possible configuration for separable object, apart from the well-known extreme case ($m_i=e_i$). In the present paper, after a brief summary of this solution, we study in some detail the coordinate systems used and the main features of the gravitational and electric fields. In particular we graph the plots of the electric force lines in three qualitatively different situations: equal-signed charges, opposite charges and the case of a naked singularity near a neutral black hole.Comment: 19 pages, 7 figures, accepted by IJMP

Nodal and Periastron Precession of Inclined Orbits in the Field of a Rotating Black Hole

The inclination of low-eccentricity orbits is shown to significantly affect the orbital parameters, in particular, the Keplerian, nodal precession, and periastron rotation frequencies, which are interpreted in terms of observable quantities. For the nodal precession and periastron rotation frequencies of low-eccentricity orbits in a Kerr field, we derive a Taylor expansion in terms of the Kerr parameter at arbitrary orbital inclinations to the black-hole spin axis and at arbitrary radial coordinates. The particle radius, energy, and angular momentum in the marginally stable circular orbits are calculated as functions of the Kerr parameter $j$ and parameter $s$ in the form of Taylor expansions in terms of $j$ to within $O[j^6]$. By analyzing our numerical results, we give compact approximation formulas for the nodal precession frequency of the marginally stable circular orbits at various $s$ in the entire range of variation of Kerr parameter.Comment: 18 pages, to be published in Astronomy Letters, 2001, vol 27 (12

Differential immuno-reactivity to genomic DNA, RNA and mitochondrial DNA is associated with auto-immunity

© 2015 S. Karger AG, Basel. Background: Circulating auto-reactive antibodies are hallmark features of auto-immune diseases, however little is known with respect to the specificity of such bio-markers. In the present study, we investigated the specificity of anti-nucleic acid antibodies in the blood of subjects with systemic lupus erythematosus (SLE) and healthy controls. Methods: Sera from 12 SLE cases and 8 controls were evaluated for immuno-reactivity to purified RNA, DNA and mitochondrial DNA (mtDNA) by enzyme-linked immuno-sorbent assay (ELISA). Results: As expected, immuno-reactivity to total nucleic acids was significantly higher in subjects with SLE when compared to healthy controls, however a clear distinction was observed among the various nucleic acid sub-types, with sera from SLE subjects displaying the greatest immuno-reactivity to RNA followed by mtDNA and then total DNA. Conclusion: The identification of auto-reactive antibodies can serve as highly sensitive biomarkers, although their specificity may not always allow diagnostic certainty. The knowledge that auto-antibodies in subjects with SLE display differential immuno-reactivity may help to improve existing diagnostics and may lead to a better understanding of the pathogenesis of auto-immune disorders

Energy Release During Disk Accretion onto a Rapidly Rotating Neutron Star

The energy release L_s on the surface of a neutron star (NS) with a weak magnetic field and the energy release L_d in the surrounding accretion disk depend on two independent parameters that determine its state (for example, mass M and cyclic rotation frequency f) and is proportional to the accretion rate. We derive simple approximation formulas illustrating the dependence of the efficiency of energy release in an extended disk and in a boundary layer near the NS surface on the frequency and sense of rotation for various NS equations of state. Such formulas are obtained for the quadrupole moment of a NS, for a gap between its surface and a marginally stable orbit, for the rotation frequency in an equatorial Keplerian orbit and in the marginally stable circular orbit, and for the rate of NS spinup via disk accretion. In the case of NS and disk counterrotation, the energy release during accretion can reach $0.67\dot{M}c^2$. The sense of NS rotation is a factor that strongly affects the observed ratio of nuclear energy release during bursts to gravitational energy release between bursts in X-ray bursters. The possible existence of binary systems with NS and disk counterrotation in the Galaxy is discussed. Based on the static criterion for stability, we present a method of constructing the dependence of gravitational mass M on Kerr rotation parameter j and on total baryon mass (rest mass) m for a rigidly rotating neutron star. We show that all global NS characteristics can be expressed in terms of the function M(j, m) and its derivatives.Comment: 42 pages, 12 figures, to appear in Astronomy Letters, 2000, v.26, p.69