On the influence of Stark broadening on Si I lines in stellar atmospheres

We study the influence of Stark broadening and stratification effects on Si\i lines in the rapidly oscillating (roAp) star 10 Aql, where the Si\i 6142.48 \AA and 6155.13 \AA lines are asymmetrical and shifted. First we have calculated Stark broadening parameters using the semiclassical perturbation method for three Si\i lines: 5950.2 \AA, 6142.48 \AA and 6155.13 \AA. We revised the synthetic sp$ calculation code taking into account both Stark width and shift for these lines. From the comparison of our calculations with the observations we found that Stark broadening + the stratification effect can explain asymmetry of the Si\i 6142.48 \AA and 6155.13 \AA lines in the atmospere of roAp star 10 Aql.Comment: Accepted to A&

The flux ratio of the [OIII] 5007,4959 lines in AGN: Comparison with theoretical calculations

By taking into account relativistic corrections to the magnetic dipole operator, the theoretical [OIII] 5006.843/4958.511 line intensity ratio of 2.98 is obtained. In order to check this new value using AGN spectra we present the measurements of the flux ratio of the [OIII] 4959,5007 emission lines for a sample of 62 AGN, obtained from the Sloan Digital Sky Survey (SDSS) Database and from published observations. We select only high signal-to-noise ratio spectra for which the line shapes of the [OIII] 4959,5007 lines are the same. We obtained an averaged flux ratio of 2.993 +/- 0.014, which is in a good agreement with the theoretical one.Comment: Accepted for publication in the MNRA

Variations of Infinite Derivative Modified Gravity

We consider nonlocal modified Einstein gravity without matter, where nonlocal term has the form $P(R) F(\Box) Q(R)$. For this model, in this paper we give the derivation of the equations of motion in detail. This is not an easy task and presented derivation should be useful to a researcher who wants to investigate nonlocal gravity. Also, we present the second variation of the related Einstein-Hilbert modified action and basics of gravity perturbations.Comment: 22 page

On the influence of Stark broadening on Cr I lines in stellar atmospheres

Using the semiclassical perturbation method, electron-, proton-, and ionized helium-impact line widths and shifts for the nine Cr I spectral lines from the $4p^7P^0-4d^7D$ multiplet, have been calculated for a perturbers density of 10$^{14}$ cm$^{-3}$ and temperatures T =2,500 - 50,000 K. The obtained results have been used to investigate the influence of Stark broadening effect in the Cr-rich Ap star $\beta$ CrB atmosphere on line shapes of these lines. It has been found that the contribution of the proton and He II collisions to the line width and shift is significant, and it is comparable and sometimes (depending of the electron temperature) even larger than electron-impact contribution. Moreover, not only the Stark line width, but, depending on the electron-, proton-, and He\ii density in stellar atmosphere also the Stark shift may contribute to the blue as well as to the red asymmetry of the same line. The obtained results have been used to investigate the influence of Stark broadening effect on line shapes of Cr\i lines in the atmosphere of Cr-rich Ap star $\beta$ CrB.Comment: 8 pages, Astron. Astrophys. accepte

Differential algebras on kappa-Minkowski space and action of the Lorentz algebra

We propose two families of differential algebras of classical dimension on kappa-Minkowski space. The algebras are constructed using realizations of the generators as formal power series in a Weyl super-algebra. We also propose a novel realization of the Lorentz algebra so(1,n-1) in terms of Grassmann-type variables. Using this realization we construct an action of so(1,n-1) on the two families of algebras. Restriction of the action to kappa-Minkowski space is covariant. In contrast to the standard approach the action is not Lorentz covariant except on constant one-forms, but it does not require an extra cotangent direction.Comment: 16 page

Star Product and Invariant Integration for Lie type Noncommutative Spacetimes

We present a star product for noncommutative spaces of Lie type, including the so called ``canonical'' case by introducing a central generator, which is compatible with translations and admits a simple, manageable definition of an invariant integral. A quasi-cyclicity property for the latter is shown to hold, which reduces to exact cyclicity when the adjoint representation of the underlying Lie algebra is traceless. Several explicit examples illuminate the formalism, dealing with kappa-Minkowski spacetime and the Heisenberg algebra (``canonical'' noncommutative 2-plane).Comment: 21 page

Fundamental Parameters of He-Weak and He-Strong Stars

We carried out low resolution spectroscopic observations in the wavelength range 3400-4700 A of 20 He-weak and 8 He-strong stars to determine their fundamental parameters by means of the Divan-Chalonge-Barbier (BCD) spectrophotometric system. For a few He-weak stars we also estimate the effective temperatures and the angular diameters by integrating absolute fluxes observed over a wide spectral range. Non-LTE model calculations are carried out to study the influence of the He/H abundance ratio on the emergent radiation of He-strong stars and on their Teff determination. We find that the effective temperatures, surface gravities and bolometric absolute magnitudes of He-weak stars estimated with the BCD system and the integrated flux method are in good agreement between each other, and they also agree with previous determinations based on several different methods. The mean discrepancy between the visual absolute magnitudes derived using the Hipparcos parallaxes and the BCD values is on average 0.3 mag for He-weak stars, while it is 0.5 mag for He-strong stars. For He-strong stars, we note that the BCD calibration, based on stars in the solar environment, leads to overestimated values of Teff. By means of model atmosphere calculations with enhanced He/H abundance ratios we show that larger He/H ratios produce smaller BD which naturally explains the Teff overestimation. We take advantage of these calculations to introduce a method to estimate the He/H abundance ratio in He-strong stars. The BD of HD 37479 suggests that the Teff of this star remains fairly constant as the star spectrum undergoes changes in the intensity of H and He absorption lines. Data for the He-strong star HD 66765 are reported for the first time.Comment: Accepted for publication in A&

Perceived need of, and interest in, HIV pre-exposure prophylaxis amongst men who have sex with men attending three sexual health clinics in London, UK

HIV pre-exposure prophylaxis (PrEP) has proven efficacy in reducing the risk of HIV infection in men who have sex with men (MSM), but has not yet been commissioned in the UK. The aim of this study was to investigate perceived need and benefit (or experience of) PrEP among HIV-negative MSM attending sexual health clinics. HIV-negative MSM attending three sexual health centres in London, UK were opportunistically invited to complete a questionnaire. Data collected comprised demographic data and sexual and drug use behaviours as well as questions regarding perceptions of risk and need for PrEP. Logistic regression analysis was undertaken to identify variables predicting acceptability of, and intention to use, PrEP. In addition, data were gathered in respondents already taking PrEP. Eight hundred and thirty-nine questionnaires were analysed. The median age of respondents was 35 years (IQR 28–41, range 18–78), 650 (77%) were of white ethnicity and 649 (77%) had a university education. Four hundred and fifty-six (54%) reported at least one episode of condomless anal sex in the preceding three months, 437 (52%) reported recreational drug use in the preceding three months and 311 (37%) had been diagnosed with a sexually transmitted infection within the preceding six months. Four hundred and sixty-three (64%) of 726 strongly agreed with the statement ‘I think I would benefit from PrEP’. Multivariate logistic regression analysis demonstrated that having receptive anal intercourse (RAI) without condoms, having an awareness of the risk of unprotected RAI and having belief in the effectiveness of PrEP were independent predictors for someone thinking they would benefit from taking PrEP. Eight percent of respondents (59/724) had already taken or were currently taking PrEP. The results suggest that individuals at risk are likely to perceive themselves as benefiting from PrEP. The majority perceived their risk of acquiring HIV and benefit from PrEP accurately. Overall they appeared to have little concern over the use of PrEP and generally positive attitudes. Further investigation is warranted to understand why those at risk do not perceive benefit from PrEP

The FERRUM project: laboratory-measured transition probabilities for Cr II

Aims: We measure transition probabilities for Cr II transitions from the z ^4H_J, z ^2D_J, y ^4F_J, and y ^4G_J levels in the energy range 63000 to 68000 cm^{-1}. Methods: Radiative lifetimes were measured using time-resolved laser-induced fluorescence from a laser-produced plasma. In addition, branching fractions were determined from intensity-calibrated spectra recorded with a UV Fourier transform spectrometer. The branching fractions and radiative lifetimes were combined to yield accurate transition probabilities and oscillator strengths. Results: We present laboratory measured transition probabilities for 145 Cr II lines and radiative lifetimes for 14 Cr II levels. The laboratory-measured transition probabilities are compared to the values from semi-empirical calculations and laboratory measurements in the literature.Comment: 13 pages. Accepted for publication in A&