Eclipsing binary statistics - theory and observation

The expected distributions of eclipse-depth versus period for eclipsing binaries of different luminosities are derived from large-scale population synthesis experiments. Using the rapid Hurley et al. BSE binary evolution code, we have evolved several hundred million binaries, starting from various simple input distributions of masses and orbit-sizes. Eclipse probabilities and predicted distributions over period and eclipse-depth (P/dm) are given in a number of main-sequence intervals, from O-stars to brown dwarfs. The comparison between theory and Hipparcos observations shows that a standard (Duquennoy & Mayor) input distribution of orbit-sizes (a) gives reasonable numbers and P/dm-distributions, as long as the mass-ratio distribution is also close to the observed flat ones. A random pairing model, where the primary and secondary are drawn independently from the same IMF, gives more than an order of magnitude too few eclipsing binaries on the upper main sequence. For a set of eclipsing OB-systems in the LMC, the observed period-distribution is different from the theoretical one, and the input orbit distributions and/or the evolutionary environment in LMC has to be different compared with the Galaxy. A natural application of these methods are estimates of the numbers and properties of eclipsing binaries observed by large-scale surveys like Gaia.Comment: 11 pages, 16 figures, accepted for publication in A&

Photo-physical properties of He-related color centers in diamond

Diamond is a promising platform for the development of technological applications in quantum optics and photonics. The quest for color centers with optimal photo-physical properties has led in recent years to the search for novel impurity-related defects in this material. Here, we report on a systematic investigation of the photo-physical properties of two He-related (HR) emission lines at 535 nm and 560 nm created in three different diamond substrates upon implantation with 1.3 MeV He+ ions and subsequent annealing. The spectral features of the HR centers were studied in an "optical grade" diamond substrate as a function of several physical parameters, namely the measurement temperature, the excitation wavelength and the intensity of external electric fields. The emission lifetimes of the 535 nm and 560 nm lines were also measured by means of time-gated photoluminescence measurements, yielding characteristic decay times of (29 +- 5) ns and (106 +- 10) ns, respectively. The Stark shifting of the HR centers under the application of an external electrical field was observed in a CVD diamond film equipped with buried graphitic electrodes, suggesting a lack of inversion symmetry in the defects' structure. Furthermore, the photoluminescence mapping under 405 nm excitation of a "detector grade" diamond sample implanted at a 1x1010 cm-2 He+ ion fluence enabled to identify the spectral features of both the HR emission lines from the same localized optical spots. The reported results provide a first insight towards the understanding of the structure of He-related defects in diamond and their possible utilization in practical applicationsComment: 9 pages, 3 figure

The Underlying Event and the Total Cross Section from Tevatron to the LHC

Multiple partonic interactions are widely used to simulate the hadronic final state in high energy hadronic collisions, and successfully describe many features of the data. It is important to make maximum use of the available physical constraints on such models, particularly given the large extrapolation from current high energy data to LHC energies. In eikonal models, the rate of multiparton interactions is coupled to the energy dependence of the total cross section. Using a Monte Carlo implementation of such a model, we study the connection between the total cross section, the jet cross section, and the underlying event. By imposing internal consistency on the model, we derive constraints on its parameters at the LHC. By imposing internal consistency on the model and comparing to current data we constrain the allowed range of its parameters. We show that measurements of the total proton-proton cross-section at the LHC are likely to break this internal consistency, and thus to require an extension of the model. Likely such extensions are that hard scatters probe a denser matter distribution inside the proton in impact parameter space than soft scatters, a conclusion also supported by Tevatron data on double-parton scattering, and/or that the basic parameters of the model are energy dependent.Comment: 17 pages, 6 figures, version accepted by JHE

Evaluation of [C(sp3)/[C(sp2)] ratio in diamondlike films through the use of a complex dielectric constant

The evaluation of the amount of tetrahedral and trigonal cross-linking, that is, the sp3- and sp2-hybridized carbon, is of great importance in understanding the properties of amorphous carbon films. In this paper we report a method for deducing the [sp3]/[sp2] ratio from the experimental values of the complex dielectric constant as obtained by optical transmittance and reflectance measurements. We assume a Gaussian-like distribution of π and π* electronic densities of states in order to fit the contribution of π→π* to the imaginary part, ε2, of the dielectric constant in the low-energy region. Through the Kramers-Kronig relationships we deduce the corresponding values of the real part ε1 of the dielectric constant for such transitions. By subtracting these values from the measured ε1 we deduce the contribution of σ→σ* to ε1. The Wemple-Didomenico model has been used to obtain the dispersion energy and the average excitation energy. Knowing the plasmon energies, we apply the ‘‘f-sum rule'' to deduce the [sp3]/[sp2] ratio. The method applied to a-C:H films deposited by rf diode sputtering provides results in agreement with those obtained by other techniques

Procedural Texture Extrapolation

We introduce a new texture basis function which generalizes noise models and can handle various kinds of spatial stochastic structures. More versatile than noise, its genericity offers improved texture authoring possibilities compared to by–example texture synthesis

Tetrahedrally bonded ternary amorphous semiconductor alloys

The properties of tetrahedrally bonded ternary amorphous semiconductors a-CSiSn:H and a-CSiGe:H are reviewed with particular emphasis on the temperature dependence of dark conductivity and the coordination in random networks. It is shown here that the dark conductivity as a function of the temperature strongly depends on the carbon content and, more precisely, on the proportion of sp3 and sp2 sites in the carbon. Ternary alloys with different carbon contents are compared to binary alloys using the average coordination number. The ternary alloys have an average coordination number close to the optimal value predicted for amorphous covalent networks

The effect of hydrogen dilution on the structure of a-C : H

Two a-C:H samples were prepared using a fast-atom deposition system from acetylene and an acetylene/hydrogen gas mixture. Their structure was investigated using neutron and x-ny diffraction and infrared spectroscopy measurements. Compositional analysis shows that a 1:1 C2H2:H-2 mixture results in a change from a-C-77:H-23 to a-C-79:H-21, i.e. has a very small effect on the composition. The diffraction data also show that the addition of hydrogen to the precursor gas has no significant effect on the average bond distances and angles but shows a small change in the H-C-H and C-C-H correlations between the two samples. However, the infrared data show that there are significant changes in the bonding of hydrogen within the sample-changes which do not affect the average network structure. We observe a decrease in the amount of sp(3) CH2 and CH3 groups, and an increase in the fraction of sp(2) and sp(3) CH groups, with the formation of a second sp(2) CH bonding environment in the hydrogen-diluted sample. Therefore, in addition to providing useful structural information on these a-C:H samples, this set of experiments illustrates very well the complementary nature of the data from diffraction and spectroscopic techniques

A spectroscopic study of the structure of amorphous hydrogenated carbon

A range of amorphous hydrogenated carbon (a-C:H) samples have been studied using inelastic neutron spectroscopy (INS) and Fourier transform infrared (FTIR) spectroscopy. Using these complementary techniques, the bonding environments of both carbon and hydrogen can be probed in some detail, with the INS data providing not only qualitative but also quantitative information. By comparing the data from each of the samples we have been able to examine the effects of different deposition conditions, i.e. precursor gas, deposition energy and deposition method, on the atomic-scale structure of a-C:H