Nature of eclipsing pulsars

We present a model for pulsar radio eclipses in some binary systems, and test this model for PSRs B1957+20 and J2051-0827. We suggest that in these binaries the companion stars are degenerate dwarfs with strong surface magnetic fields. The magnetospheres of these stars are permanently infused by the relativistic particles of the pulsar wind. We argue that the radio waves emitted by the pulsar split into the eigenmodes of the electron-positron plasma as they enter the companion's magnetosphere and are then strongly damped due to cyclotron resonance with the ambient plasma particles. Our model explains in a natural way the anomalous duration and behavior of radio eclipses observed in such systems. In particular, it provides stable, continuous, and frequency-dependent eclipses, in agreement with the observations. We predict a significant variation of linear polarization both at eclipse ingress and egress. In this paper we also suggest several possible mechanisms of generation of the optical and $X$-ray emission observed from these binary systems.Comment: 12 pages, 5 figures, submitted to Ap

Technique of electrical stimulation of the vestibular analyzer under clinical conditions

Vestibular reactions appear under the action of direct current (dc) on the labyrinth of man and animals. A decrease of the stimulation effect of dc on the extralabyrinthine nervous formations in the suggested method is achieved by the use of electric pulses with steep front and back parts, as well as by previous anesthetization of the skin in the electrode application area by means of novocain solution electrophoresis. For this purpose a pulse producer giving trapezoid pulses with smoothly changing fronts and duration was constructed. With the help of an interrupter it is possible to stop the current increase instantly, and stimulation is performed at the level of the pulse 'plateau'. To induce vestibular reactions under monopolar stimulation, it is necessary to apply the current twice as high as that with bipolar electrode position. The use of short pulses with steep front and back parts for electrode stimulation of the vestibular analyzer is considered to be inexpedient

Spectrum evolution in binary pulsar B1259-63/LS 2883 Be star and gigahertz-peaked spectra

We study the radio spectrum of PSR B1259-63 orbiting around the Be star LS 2883 and show that the shape of the spectrum depends on the orbital phase. At frequencies below 3 GHz PSR B1259-63 flux densities are lower when measured near the periastron passage than those measured far from periastron. We suggest that an interaction of the radio waves with the Be star environment accounts for this effect. While it is quite natural to explain the pulsar eclipse by the presence of an equatorial disk around LS 2883, this disk alone cannot be responsible for the observed spectral evolution of PSR B1259-63 and we, therefore, propose a qualitative model which explains this evolution. We consider two mechanisms that might influence the observed radio emission: free-free absorption and cyclotron resonance. We believe that this binary system can hold the clue to the understanding of gigahertz-peaked spectra of pulsars.Comment: 5 pages, 4 figures, MNRAS Letters, 418, L114-L118 (2011

Risk factors and algorithms to identify hepatitis C, hepatitis B, and HIV among Georgian tuberculosis patients

SummaryObjectivesTo determine prevalence, risk factors, and simple identification algorithms for HIV, hepatitis B, and hepatitis C co-infection; factors that may predispose for anti-tuberculosis therapy-induced hepatotoxicity.MethodsWe recruited 300 individuals at in-patient tuberculosis hospitals in three cities in Georgia, administered a behavioral questionnaire, and tested for antibody to HIV, hepatitis C (HCV), hepatitis B core antigen (anti-HBc), and the hepatitis B surface antigen (HBsAg).ResultsOf the individuals tested, 0.7% were HIV positive, 4.3% were HBsAg positive, 8.7% were anti-HBc positive, and 12.0% were HCV positive. In multivariable analysis, a history of blood transfusion, injection drug use, and prison were significant independent risk factors for HCV, while a history of blood transfusion, injection drug use, younger age at sexual debut, and a high number of sex partners were significant risk factors for HBV. Three-questionnaire item algorithms predicted HCV serostatus 74.1% of the time and HBV serostatus 85.2% of the time.ConclusionsTreatment of tuberculosis patients in resource-limited countries with concurrent epidemics of HCV, HBV, and HIV may be associated with significant hepatotoxicity. Serologic screening of tuberculosis patients for HBV, HCV, and HIV or using behavioral algorithms to identify patients in need of intensive monitoring during anti-tuberculosis therapy may reduce this risk

Cigarette smoking among school teachers in Tobago

Khechinashvili G, Andall-Brereton G, Razum O. Cigarette smoking among school teachers in Tobago. WEST INDIAN MEDICAL JOURNAL. 2004;53(4):260-262.Tobago, until lately, was considered a society with a low prevalence of cigarette smoking. Recent surveys, however, showed an increasing smoking prevalence among school children. To assess whether teachers in Tobago can be credible role models for their pupils, we carried out a cross-sectional survey on their smoking-related attitudes and behaviour in 2002. We distributed anonymous, structured questionnaires to teachers of all 52 primary and secondary schools in the island and conducted structured observations in schools. Of 579 teachers present during the survey, 559 (97%) returned a completed questionnaire; 8.6% of the male and 2.4% of the female teachers reported to be current cigarette smokers; slightly higher proportions had ever been daily smokers. Teachers were well aware of the harmful effects of smoking. Significantly more non-smokers than current smokers were in favour of strict school smoking regulations. The vast majority of the teachers perceived anti-smoking education as their duty. None of the schools had dedicated smoking rooms for teachers, and we found no cigarette butts in or around teachers' rooms. In Tobago, teachers have a lower reported prevalence of cigarette smoking than their pupils. Thus, most teachers can be credible role models with regard to smoking prevention and should be encouraged to become more active in school-based preventive activities