High-precision acoustic helium signatures in 18 low-mass low-luminosity red giants. Analysis from more than four years of Kepler observations

High-precision frequencies of acoustic modes in red giant stars are now available thanks to the long observing length and high-quality of the light curves provided by the NASA Kepler mission, thus allowing to probe the interior of evolved cool low-mass stars with unprecedented level of detail. We characterize the acoustic signature of the helium second ionization zone in a sample of 18 low-mass low-luminosity red giants by exploiting new mode frequency measurements derived from more than four years of Kepler observations. We analyze the second frequency differences of radial acoustic modes in all the stars of the sample by using the Bayesian code Diamonds. We find clear acoustic glitches due to the signature of helium second ionization in all the stars of the sample. We measure the acoustic depth and the characteristic width of the acoustic glitches with a precision level on average around $\sim$2% and $\sim$8%, respectively. We find good agreement with theoretical predictions and existing measurements from the literature. Lastly, we derive the amplitude of the glitch signal at $\nu_\mathrm{max}$ for the second differences and for the frequencies with an average precision of $\sim$6%, obtaining values in the range 0.14-0.24 $\mu$Hz, and 0.08-0.33 $\mu$Hz, respectively, which can be used to investigate the helium abundance in the stars.Comment: 12 pages, 19 figures, 3 tables. Accepted for publication in A&

Bayesian peak bagging analysis of 19 low-mass low-luminosity red giants observed with Kepler

The currently available Kepler light curves contain an outstanding amount of information but a detailed analysis of the individual oscillation modes in the observed power spectra, also known as peak bagging, is computationally demanding and challenging to perform on a large number of targets. Our intent is to perform for the first time a peak bagging analysis on a sample of 19 low-mass low-luminosity red giants observed by Kepler for more than four years. This allows us to provide high-quality asteroseismic measurements that can be exploited for an intensive testing of the physics used in stellar structure models, stellar evolution and pulsation codes, as well as for refining existing asteroseismic scaling relations in the red giant branch regime. For this purpose, powerful and sophisticated analysis tools are needed. We exploit the Bayesian code Diamonds, using an efficient nested sampling Monte Carlo algorithm, to perform both a fast fitting of the individual oscillation modes and a peak detection test based on the Bayesian evidence. We find good agreement for the parameters estimated in the background fitting phase with those given in the literature. We extract and characterize a total of 1618 oscillation modes, providing the largest set of detailed asteroseismic mode measurements ever published. We report on the evidence of a change in regime observed in the relation between linewidths and effective temperatures of the stars occurring at the bottom of the RGB. We show the presence of a linewidth depression or plateau around $\nu_\mathrm{max}$ for all the red giants of the sample. Lastly, we show a good agreement between our measurements of maximum mode amplitudes and existing maximum amplitudes from global analyses provided in the literature, useful as empirical tools to improve and simplify the future peak bagging analysis on a larger sample of evolved stars.Comment: 78 pages, 46 figures, 22 tables. Accepted for publication in A&

Profit efficiency among Kenyan smallholders milk producers: A case study of Meru-South district, Kenya

Production inefficiency is usually analyzed by economical efficiency, which is composed of two components-technical and allocative efficiencies. This study provided a direct measure of production efficiency of the smallholder milk producers in Kenya using a stochastic profit frontier and inefficiency model. The primary data were collected, using IMPACT (intergrated modeling platform for mixed animal crops systems) structured questionnaire and includes four conventional inputs and socio-economic factors affecting production. The result showed that profit efficiencies of the sampled farmers varied widely between 26% and 73% with a mean of 60% suggesting that an estimated 40% of the profit is lost due to a combination of both technical and allocative inefficiencies in the smallholder dairy milk production. This study further observed that level of education, experience, and the size of the farm influenced profit efficiency positively while profit efficiency decreased with age. This implies that profit inefficiency among smallholder dairy milk producers can be reduced significantly with improvement in the level of education of sampled farmer

Alignment issues in photonic crystal device fabrication

An important requirement in the fabrication of photonic crystal structures is the correct relative alignment of structural elements. Accuracy should be in the order of some tens of nanometres. Some of the options for providing such accuracy are discussed. Examples are given of aligning defects with respect to a predefined 2D lattice, aligning access waveguides with respect to a small local photonic crystal structure, and the alignment of successive periodically structured layers in a 3D "woodpile" structure

The ring-opening polymerization of D,L-lactide in the melt initiated with tetraphenyltin

Melt polymerization conditions for D,L-lactide initiated with tetraphenyltin were studied with regard to polymer molecular weight and weight distributions. "Single" polymerization, "multiple"polymerization (four or eight reactions at the same time), and time-dependent studies are described. Single polymerizations using constant initiator concentrations resulted in a broad scattering of nonreproducible molecular weight values. Multiple polymerizations at constant initiator concentrations, however, resulted in nearly identical molecular weight profiles. Multiple polymerizations at different initiator concentrations did not show an inverse dependency of initiator concentration on polymer molecular weight. Both the single and multiple melt polymerizations resulted in rather broad molecular weight distributions. The presence of hydrolysis products of lactide during the melt polymerization most likely has a detrimental effect on molecular weight. After a short induction period the rather slow polymerization of D,L-lactide resulted in a maximal molecular weight followed by a slight decrease in molecular weight to a constant value. It is concluded that the polymerization of D,L-lactide in the melt initiated with tetraphenyltin does not proceed through a "living" mechanism

Towards the re-verification of process tank calibrations

Re-verification is needed to ensure that the calibration (the relationship between measured level and measured volume) that is obtained during commissioning hasn’t changed over time. This can be achieved, in part, by metering in solution and correlating with marks identified a priori. Mark identification and correlation are discussed and possible error sources are outlined

QCD at Photon Colliders

The novel possibilities of probing the photon structure and high energy limit of QCD at photon colliders are summarised. We discuss the photon structure function $F_2^{\gamma}(x,Q^2)$, the gluon distribution in the photon and the spin dependent structure function $g_1^{\gamma}(x,Q^2)$ of the photon and emphasise advantages of the photon colliders for measuring these quantities. The possibility of probing the QCD pomeron and odderon in $\gamma\gamma$ and $e \gamma$ collisions is also described.Comment: 14 pages with 3 postscript figures included, introductory talk given at the International Workshop on High Energy Photon Colliders, 14th - 17th June 2000, DESY, Hamburg, German