A method to determine the parameters of black holes in AGNs and galactic X-ray sources with periodic modulation of variability

We propose a simple and unambiguous way to deduce the parameters of black holes which may reside in AGNs and some types of X-ray binaries. The black-hole mass and angular momentum are determined in physical units. The method is applicable to the sources with periodic components of variability, provided one can assume the following: (i) Variability is due to a star or a stellar-mass compact object orbiting the central black hole and passing periodically through an equatorial accretion disk (variability time-scale is given by the orbital period). (ii) The star orbits almost freely, deviation of its trajectory due to passages through the disk being very weak (secular); the effect of the star on the disk, on the other hand, is strong enough to yield observable photometric and spectroscopic features. (iii) The gravitational field within the nucleus is that of the (Kerr) black hole, the star and the disk contribute negligibly.Comment: 17 pages, 4 figures, 2 tables; LaTeX2.09 (aas2pp4.sty); submitted to the Astrophysical Journal; also available at http://astro.mff.cuni.cz/karas/papers.htm with additional illustration

Advances in the management of HPV-related oropharyngeal cancer

Patients with human papillomavirus- (HPV-) related oropharyngeal squamous cell carcinoma (OPSCC) have a better prognosis than HPV-negative OPSCC when treated with standard high-dose cisplatin-based chemoradiotherapy. Consistent with this assertion and due to younger age at diagnosis, novel approaches tominimize treatment sequelaewhile preserving survival outcomes become of paramount importance. Here, we critically reviewed the evidence-based literature supporting the deintensification strategies in HPV-related OPSCC management, including radiotherapy dose and/or volume reduction, replacement of cisplatin radiosensitising chemotherapy, and the use of transoral surgery. Undoubtedly, further researches are needed before changing the standard of care in this setting of patients

Excess of weight: is it a modifiable predictive and prognostic factor in locally advanced rectal cancer?

To evaluate the relationship between body mass index (BMI) and rates of treatment tolerance and clinical outcomes in patients with locally advanced rectal cancer treated with a multimodality approach. PATIENTS AND METHODS: This study was conducted on 56 patients with histologically proven rectal adenocarcinoma, staged T3-4, and/or node-positive tumor, which underwent intensified radiochemotherapy (RT-CHT) treatment before surgery. We calculated adiposity indices and analyzed their influence on treatment tolerance and clinical outcomes. RESULTS: Distribution of the 56 patients according to BMI was BMI < 25 kg/m2 (n = 19; 33.9%), BMI 25-29 kg/m2 (n = 29; 51.8%) and BMI ≥ 30 kg/m2 (n = 8; 14.3%). BMI had no significant influence on neo-adjuvant treatment-related toxicity. With a median follow-up of 23 months (range 11-47), the 2-year survival was 85.7%. We did not observe any significant difference among the three BMI categories for any of the outcomes. CONCLUSIONS: This study suggested no evident links between overweight and survival in patients with locally advanced rectal carcinoma treated with neo-adjuvant RT-CHT. Overweight patients tolerate treatment as normal-weight patients

Collimation of a spherical collisionless particles stream in Kerr space-time

We examine the propagation of collisionless particles emitted from a spherical shell to infinity. The number distribution at infinity, calculated as a function of the polar angle, exhibits a small deviation from uniformity. The number of particles moving from the polar region toward the equatorial plane is slightly larger than that of particles in the opposite direction, for an emission radius $> 4.5M$ in extreme Kerr space-time. This means that the black hole spin exerts an anti-collimation effect on the particles stream propagating along the rotation axis. We also confirm this property in the weak field limit. The quadrupole moment of the central object produces a force toward the equatorial plane. For a smaller emission radius $r<4.5M$, the absorption of particles into the black hole, the non-uniformity and/or the anisotropy of the emission distribution become much more important.Comment: 11 pages, 8 figures; accepted for publication in CQ

Physical properties of Tolman-Bayin solutions: some cases of static charged fluid spheres in general relativity

In this article, Einstein-Maxwell space-time has been considered in connection to some of the astrophysical solutions as previously obtained by Tolman (1939) and Bayin (1978). The effect of inclusion of charge into these solutions has been investigated thoroughly and also the nature of fluid pressure and mass density throughout the sphere have been discussed. Mass-radius and mass-charge relations have been derived for various cases of the charged matter distribution. Two cases are obtained where perfect fluid with positive pressures give rise to electromagnetic mass models such that gravitational mass is of purely electromagnetic origin.Comment: 15 pages, 12 figure

Charge, geometry, and effective mass in the Kerr-Newman solution to the Einstein field equations

It has been shown that for the Reissner-Nordstrom solution to the vacuum Einstein field equations charge, like mass, has a unique space-time signature [Found. Phys. 38, 293-300 (2008)]. The presence of charge results in a negative curvature. This work, which includes a discussion of effective mass, is extended here to the Kerr-Newman solution.Comment: To appear in Foundations of Physics. Misprints have been corrected. 14 pages, 4 figure

The finite index basis property

We describe in this paper a connection between bifix codes, symbolic dynamical systems and free groups. This is in the spirit of the connection established previously for the symbolic systems corresponding to Sturmian words. We introduce a class of sets of factors of an infinite word with linear factor complexity containing Sturmian sets and regular interval exchange sets, namely the class of tree sets. We prove as a main result that for a uniformly recurrent tree set S, a finite bifix code X on the alphabet A is S-maximal of S-degree d if and only if it is the basis of a subgroup of index d of the free group on