Prospect on intergalactic magnetic field measurements with gamma-ray instruments

Observing high-energy gamma-rays from Active Galactic Nuclei (AGN) offers a unique potential to probe extremely tiny values of the intergalactic magnetic field (IGMF), a long standing question of astrophysics, astropa rticle physics and cosmology. Very high energy (VHE) photons from blazars propagating along the line of sight interact with the extragalactic background light (EBL) and produce e + e − pairs. Through inverse-Compton interaction, mainly on the cosmic microwave background (CMB), these pairs generate secondary GeV-TeV compo- nents accompanying the primary VHE signal. Such secondary components would be detected in the gamma-ray range as delayed “pair echos” for very weak IGMF ( B< 10 − 16 G ), while they should result in a spatially extended ga mma-ray emission around the source for higher IGMF values ( B> 10 − 16 G ). Coordinated observations with space (i.e. Fermi) and ground- based gamma-ray instruments, such as the pre sent Cherenkov experiments H.E.S.S., MAGIC and VERITAS, the future Cherenkov Telescope Array (CTA) Observatory, and the wide-field detectors such as HAWC and LHAASO, should allow to analyze and finally detect such echos, extended emission or pair halos, and to further characterize the IGMF.

Simple heuristics for the assembly line worker assignment and balancing problem

We propose simple heuristics for the assembly line worker assignment and balancing problem. This problem typically occurs in assembly lines in sheltered work centers for the disabled. Different from the well-known simple assembly line balancing problem, the task execution times vary according to the assigned worker. We develop a constructive heuristic framework based on task and worker priority rules defining the order in which the tasks and workers should be assigned to the workstations. We present a number of such rules and compare their performance across three possible uses: as a stand-alone method, as an initial solution generator for meta-heuristics, and as a decoder for a hybrid genetic algorithm. Our results show that the heuristics are fast, they obtain good results as a stand-alone method and are efficient when used as a initial solution generator or as a solution decoder within more elaborate approaches.

Studying the genetic basis of drought tolerance in sorghum by managed stress trials and adjustments for phenological and plant height differences

Managed environments in the form of well watered and water stressed trials were performed to study the genetic basis of grain yield and stay green in sorghum with the objective of validating previously detected QTL. As variations in phenology and plant height may influence QTL detection for the target traits, QTL for flowering time and plant height were introduced as cofactors in QTL analyses for yield and stay green. All but one of the flowering time QTL were detected near yield and stay green QTL. Similar co-localization was observed for two plant height QTL. QTL analysis for yield, using flowering time/plant height cofactors, led to yield QTL on chromosomes 2, 3, 6, 8 and 10. For stay green, QTL on chromosomes 3, 4, 8 and 10 were not related to differences in flowering time/plant height. The physical positions for markers in QTL regions projected on the sorghum genome suggest that the previously detected plant height QTL, Sb-HT9-1, and Dw2, in addition to the maturity gene, Ma5, had a major confounding impact on the expression of yield and stay green QTL. Co-localization between an apparently novel stay green QTL and a yield QTL on chromosome 3 suggests there is potential for indirect selection based on stay green to improve drought tolerance in sorghum. Our QTL study was carried out with a moderately sized population and spanned a limited geographic range, but still the results strongly emphasize the necessity of corrections for phenology in QTL mapping for drought tolerance traits in sorghum.

The relationship between gamma Cassiopeiae's X-ray emission and its circumstellar environment

gamma Cas is the prototypical classical Be star and is recently best known for its variable hard X-ray emission. To elucidate the reasons for this emission, we mounted a multiwavelength campaign in 2010 centered around four XMM-Newton observations. The observational techniques included long baseline optical interferometry (LBOI) from two instruments at CHARA, photometry carried out by an automated photometric telescope and H alpha observations. Because gamma Cas is also known to be in a binary, we measured radial velocities from the H alpha line and redetermined its period as 203.55 +/- 0.20 days and its eccentricity as near zero. The LBOI observations suggest that the star's decretion disk was axisymmetric in 2010, has an system inclination angle near 45 degrees, and a larger radius than previously reported. In addition, the Be star began an "outburst" at the beginning of our campaign, made visible by a brightening and reddening of the disk during our campaign and beyond. Our analyses of the new high resolution spectra disclosed many attributes also found from spectra obtained in 2001 (Chandra) and 2004 (XMM-Newton). As well as a dominant hot (approximate to 14 keV) thermal component, the familiar attributes included: (i) a fluorescent feature of Fe K even stronger than observed at previous times; (ii) strong lines of N VII and Ne XI lines indicative of overabundances; and (iii) a subsolar Fe abundance from K-shell lines but a solar abundance from L-shell ions. We also found that two absorption columns are required to fit the continuum. While the first one maintained its historical average of 1 x 10(21) cm(-2), the second was very large and doubled to 7.4 x 10(23) cm(-2) during our X-ray observations. Although we found no clear relation between this column density and orbital phase, it correlates well with the disk brightening and reddening both in the 2010 and earlier observations. Thus, the inference from this study is that much (perhaps all?) of the X-ray emission from this source originates behind matter ejected by gamma Cas into our line of sight.