Composite fields, generalized hypergeometric functions and the U(1)YU(1)_Y symmetry in the AdS/CFT correspondence

We discuss the concept of composite fields in flat CFT as well as in the context of AdS/CFT. Furthermore we show how to represent Green functions using generalized hypergeometric functions and apply these techniques to four-point functions. Finally we prove an identity of $U(1)_Y$ symmetry for four-point functions.Comment: 12 pages, 2 figure

Carbon line formation and spectroscopy in O-type stars

The determination of chemical abundances constitutes a fundamental requirement for obtaining a complete picture of a star. Particularly in massive stars, CNO abundances are of prime interest, due to the nuclear CNO-cycle and various mixing processes which bring these elements to the surface. We aim at enabling a reliable carbon spectroscopy for our unified NLTE atmosphere code FASTWIND. We develop a new carbon model atom including CII/III/IV/V, and discuss problems related to carbon spectroscopy in O-type stars. We describe different tests to examine the reliability of our implementation, and investigate which mechanisms influence the carbon ionization balance. By comparing with high-resolution spectra from six O-type stars, we check in how far observational constraints can be reproduced by our new carbon line synthesis. Carbon lines are even more sensitive to a variation of temperature, gravity, and mass-loss rate, than hydrogen/helium lines. We are able to reproduce most of the observed lines from our stellar sample, and to estimate those specific carbon abundances which bring the lines from different ions into agreement. For hot dwarfs and supergiants earlier than O7, X-rays from wind-embedded shocks can impact the synthesized line strengths, particularly for CIV, potentially affecting the abundance determination. We have demonstrated our capability to derive realistic carbon abundances by means of FASTWIND, using our recently developed model atom. We found that complex effects can have a strong influence on the carbon ionization balance in hot stars. For a further understanding, the UV range needs to be explored as well. By means of detailed nitrogen and oxygen model atoms available to use, we will be able to perform a complete CNO abundance analysis for larger samples of massive stars, and to provide constraints on corresponding evolutionary models and aspects.Comment: 22 pages, 16 figures, 6 table

Radiation-driven winds of hot luminous stars. XVI. Expanding atmospheres of massive and very massive stars and the evolution of dense stellar clusters

Context: Starbursts, and particularly their high-mass stars, play an essential role in the evolution of galaxies. The winds of massive stars not only significantly influence their surroundings, but the mass loss also profoundly affects the evolution of the stars themselves. In addition to the evolution of each star, the evolution of the dense cores of massive starburst clusters is affected by N-body interactions, and the formation of very massive stars via mergers may be decisive for the evolution of the cluster. Aims: To introduce an advanced diagnostic method of O-type stellar atmospheres with winds, including an assessment of the accuracy of the determinations of abundances, stellar and wind parameters. Methods: We combine consistent models of expanding atmospheres with detailed stellar evolutionary calculations of massive and very massive single stars with regard to the evolution of dense stellar clusters. Accurate predictions of the mass loss rates of very massive stars requires a highly consistent treatment of the statistical equilibrium and the hydrodynamic and radiative processes in the expanding atmospheres. Results: We present computed mass loss rates, terminal wind velocities, and spectral energy distributions of massive and very massive stars of different metallicities, calculated from atmospheric models with an improved level of consistency. Conclusions: Stellar evolutionary calculations using our computed mass loss rates show that low-metallicity very massive stars lose only a very small amount of their mass, making it unlikely that very massive population III stars cause a significant helium enrichment of the interstellar medium. Solar-metallicity stars have higher mass-loss rates, but these are not so high to exclude very massive stars formed by mergers in dense clusters from ending their life massive enough to form intermediate-mass black holes.Comment: Accepted by A&

Numerical Models for the Diffuse Ionized Gas in Galaxies. II. Three-dimensional radiative transfer in inhomogeneous interstellar structures as a tool for analyzing the diffuse ionized gas

Aims: We systematically explore a plausible subset of the parameter space involving effective temperatures and metallicities of the ionizing stellar sources, the effects of the hardening of their radiation by surrounding leaky HII regions with different escape fractions, as well as different scenarios for the clumpiness of the DIG, and compute the resulting line strength ratios for a number of diagnostic optical emission lines. Methods: For the ionizing fluxes we compute a grid of stellar spectral energy distributions (SEDs) from detailed, fully non-LTE model atmospheres that include the effects of stellar winds and line blocking and blanketing. To calculate the ionization and temperature structure in the HII regions and the diffuse ionized gas we use spherically symmetric photoionization models as well as state-of-the-art three-dimensional (3D) non-LTE radiative transfer simulations, considering hydrogen, helium, and the most abundant metals. Results: We provide quantitative predictions of how the line ratios from HII regions and the DIG vary as a function of metallicity, stellar effective temperature, and escape fraction from the HII region. The range of predicted line ratios reinforces the hypothesis that the DIG is ionized by (filtered) radiation from hot stars; however, comparison of observed and predicted line ratios indicates that the DIG is typically ionized with a softer SED than predicted by the chosen stellar population synthesis model. Even small changes in simulation parameters like the clumping factor can lead to considerable variation in the ionized volume. Both for a more homogeneous gas and a very inhomogeneous gas containing both dense clumps and channels with low gas density, the ionized region in the dilute gas above the galactic plane can cease to be radiation-bounded, allowing the ionizing radiation to leak into the intergalactic medium.Comment: 21 pages, 9 figures, accepted by A&

Atmospheric NLTE-Models for the Spectroscopic Analysis of Blue Stars with Winds. III. X-ray emission from wind-embedded shocks

X-rays/EUV radiation emitted from wind-embedded shocks in hot, massive stars can affect the ionization balance in their outer atmospheres, and can be the mechanism responsible for the production of highly ionized species. To allow for these processes in the context of spectral analysis, we have implemented such emission into our unified, NLTE model atmosphere/spectrum synthesis code FASTWIND. The shock structure and corresponding emission is calculated as a function of user-supplied parameters. We account for a temperature and density stratification inside the post-shock cooling zones, calculated for radiative and adiabatic cooling in the inner and outer wind, respectively. The high-energy absorption of the cool wind is considered by adding important K-shell opacities, and corresponding Auger ionization rates have been included into the NLTE network. We tested and verified our implementation carefully against corresponding results from various alternative model atmosphere codes, and studied the effects from shock emission for important ions from He, C, N, O, Si, and P. Surprisingly, dielectronic recombination turned out to play an essential role for the ionization balance of OIV/OV around Teff = 45,000 K. Finally, we investigated the behavior of the mass absorption coefficient, kappa_nu(r), important in the context of X-ray line formation in massive star winds. In almost all considered cases, direct ionization is of major influence, and Auger ionization significantly affects only NVI and OVI. The approximation of a radially constant kappa_nu is justified for r > 1.2 Rstar and lambda < 18 A, and also for many models at longer wavelengths. To estimate the actual value of this quantity, however, the HeII opacities need to be calculated from detailed NLTE modeling, at least for wavelengths longer than 18 to 20 A, and information on the individual CNO abundances has to be present.Comment: accepted by A&

Non-LTE models for synthetic spectra of type Ia supernovae. III. An accelerated lambda iteration procedure for the mutual interaction of strong spectral lines in SN Ia models with and without energy deposition

Context. Spectroscopic analyses to interpret the spectra of the brightest supernovae from the UV to the near-IR provide a powerful tool with great astrophysical potential for the determination of the physical state of the ejecta, their chemical composition, and the SNe distances even at significant redshifts. Methods. We report on improvements of computing synthetic spectra for SNIa with respect to i) an improved and sophisticated treatment of thousands of strong lines that interact intricately with the "pseudo-continuum" formed entirely by Doppler- shifted spectral lines, ii) an improved and expanded atomic database, and iii) the inclusion of energy deposition within the ejecta. Results. We show that an accelerated lambda iteration procedure we have developed for the mutual interaction of strong spectral lines appearing in the atmospheres of SNeIa solves the longstanding problem of transferring the radiative energy from the UV into the optical regime. In detail we discuss applications of the diagnostic technique by example of a standard SNIa, where the comparison of calculated and observed spectra revealed that in the early phases the consideration of the energy deposition within the spectrum-forming regions of the ejecta does not qualitatively alter the shape of the spectra. Conclusions. The results of our investigation lead to an improved understanding of how the shape of the spectrum changes radically as function of depth in the ejecta, and show how different emergent spectra are formed as a result of the particular physical properties of SNe Ia ejecta and the resulting peculiarities in the radiative transfer. This provides an important insight into the process of extracting information from observed SNIa spectra, since these spectra are a complex product of numerous unobservable SNIa spectral features which are thus analyzed in parallel to the observable spectral features.Comment: 27 pages, 19 figures. Submitted to A&A, revised versio

Telehealth methods to deliver multifactorial dietary interventions in adults with chronic disease: A systematic review protocol

Background: The long-term management of chronic diseases requires adoption of complex dietary recommendations, which can be facilitated by regular coaching to support sustained behaviour change. Telehealth interventions can overcome patient-centred barriers to accessing face-to-face programs and provide feasible delivery methods, ubiquitous and accessible regardless of geographic location. The protocol for this systematic review explains the methods that will be utilised to answer the review question of whether telehealth interventions are effective at promoting change in dietary intake and improving diet quality in people with chronic disease. Methods/design: A structured search of Medline, EMBASE, CINAHL, and PsychINFO, from their inception, will be conducted. We will consider randomised controlled trials which evaluate complex dietary interventions in adults with chronic disease. Studies must provide diet education in an intervention longer than 4 weeks in duration, and at least half of the intervention contact must be delivered via telehealth. Comparisons will be made against usual care or a non-telehealth intervention. The primary outcome of interest is dietary change with secondary outcomes relating to clinical markers pre-specified in the methodology. The process for selecting studies, extracting data, and resolving conflicts will follow a set protocol. Two authors will independently appraise the studies and extract the data, using specified methods. Meta-analyses will be conducted where appropriate, with parameters for determining statistical heterogeneity pre-specified. The GRADE tool will be used for determining the quality of evidence for analysed outcomes. Discussion: To date, there has been a considerable variability in the strategies used to deliver dietary education, and the overall effectiveness of telehealth dietary interventions for facilitating dietary change has not been reviewed systematically in adults with chronic disease. A systematic synthesis of telehealth strategies will inform the development of evidence-based telehealth programs that can be tailored to deliver dietary interventions specific to chronic disease conditions. Systematic review registration: PROSPERO CRD42015026398

Sol-Gel Derived Ferroelectric Nanoparticles Investigated by Piezoresponse Force Microscopy

Piezoresponse force microscopy (PFM) was used to investigate the ferroelectric properties of sol-gel derived LiNbO$_3$ nanoparticles. To determine the degree of ferroelectricity we took large-area images and performed statistical image-analysis. The ferroelectric behavior of single nanoparticles was verified by poling experiments using the PFM tip. Finally we carried out simultaneous measurements of the in-plane and the out-of-plane piezoresponse of the nanoparticles, followed by measurements of the same area after rotation of the sample by 90$^{\circ}$ and 180$^{\circ}$. Such measurements basically allow to determine the direction of polarization of every single particle