4,967 research outputs found
A new function of hydrocarbons in insect communication : maternal care and offspring signalling in the European earwig
International audienc
A continuous low star formation rate in IZw 18 ?
Deep long-slit spectroscopic observations of the blue compact galaxy IZw 18
obtained with the CFH 3.6 m Telescope are presented. The very low value of
oxygen abundance previously reported is confirmed and a very homogeneous
abundance distribution is found (no variation larger than 0.05 dex) over the
whole ionized region. We concur with Tenorio-Tagle (1996) and Devost et al.
(1997) that the observed abundance level cannot result from the material
ejected by the stars formed in the current burst, and propose that the observed
metals were formed in a previous star formation episode. Metals ejected in the
current burst of star formation remain most probably hidden in a hot phase and
are undetectable using optical spectroscopy. We discuss different scenarios of
star formation in IZw 18. Combining various observational facts, for instance
the faint star formation rate observed in low surface brightness galaxies van
Zee et al. (1997), it is proposed that a low and continuous rate of star
formation occurring during quiescent phases between bursts could be a
significant source of metal enrichment of the interstellar medium.Comment: 10 pages, 4 Postscript figures, to be published in Astronomy and
Astrophysics main journa
Autonomous Guidance of a Corn Harvester using Stereo Vision
Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is a paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 9 (2007): Autonomous Guidance of a Corn Harvester using Stereo Vision. Manuscript ATOE 07 013. Vol. IX. July, 2007
Collaborative Engineering: An Airbus Case Study
AbstractThis document introduces the main concepts of Collaborative Engineering as a new methodology, procedures and tools to design and develop an aircraft, as Airbus Military is implementing.Airbus designs and industrializes aircrafts under Concurrent Engineering techniques since decades with success. The introduction of new PLM methodologies, procedures and tools, mainly in the industrialization areas, and the need to reduce time-to-market conducted Airbus Military to push the engineering teams to do things in a different way.Traditional Engineering works sequentially, Concurrent Engineering basically overlaps tasks between teams using maturity states and taking assuming risks. Collaborative Engineering promotes a single team to develop product, processes and resources from the conceptual phase to the start of the serial production. The deliverable of the team is an iDMU (industrial DMU), a complete definition and verification of the virtual manufacturing of the product
The effect of collisional enhancement of Balmer lines on the determination of the primordial helium abundance
This paper describes a new determination of the primordial helium abundance
(Y_P), based on the abundance analysis of five metal-poor extragalactic HII
regions. For three regions of the sample (SBS 0335-052, I Zw 18, and H29) we
present tailored photoionization models based on improved calculations with
respect to previous models. In particular, we use the photoionization models to
study quantitatively the effect of collisional excitation of Balmer lines on
the determination of the helium abundance (Y) in the individual regions. This
effect is twofold: first, the intensities of the Balmer lines are enhanced with
respect to the pure recombination value, mimicking a higher hydrogen abundance;
second, the observed reddening is larger than the true extinction, due to the
differential effect of collisions on different Balmer lines. In addition to
these effects, our analysis takes into account the following features of HII
regions: (i) the temperature structure, (ii) the density structure, (iii) the
presence of neutral helium, (iv) the collisional excitation of the HeI lines,
(v) the underlying absorption of the HeI lines, and (vi) the optical thickness
of the HeI lines. The object that shows the highest increase in Y after the
inclusion of collisional effects in the analysis is SBS 0335-052, whose helium
abundance has been revised by Delta Y = +0.0107. The revised Y values for the
five objects in our sample yield an increase of +0.0035 in Y_P, giving Y_P =
0.2391 +/- 0.0020.Comment: 59 pages, 8 figures. AAS Latex. Accepted for publication in the
Astrophysical Journa
Implementation of the iDMU for an Aerostructure Industrialization in AIRBUS
AbstractAIRBUS Military has undertaken a project to implement the industrial Digital Mock-Up (iDMU) concept to support the industrialization process of a medium size aerostructure. Within the framework of a collaborative engineering strategy, such project is part of the efforts to deploy Digital Manufacturing as a key technology for the industrialization of aircrafts assembly lines. The project has confirmed the potential of the iDMU to improve the industrial design process in a collaborative engineering environment. This communication presents the main project objectives, the key methodological points, the main project achievements and the next additional developments to increase the scope and benefits of the iDMU concept
M onitoring land-cover changes: a com parison of change detection techniques*
Abstract. Six change detection procedures were tested using Landsat MultiSpectral Scanner (MSS) images for detecting areas of changes in the region of the Te  rminos Lagoon, a coastal zone of the State of Campeche, Mexico. The change detection techniques considered were image di erencing, vegetative index di erencing, selective principal components analysis (SPCA), direct multi-date unsupervised classi® cation, post-classi® cation change di erencing and a combination of image enhancement and post-classi® cation comparison. The accuracy of the results obtained by each technique was evaluated by comparison with aerial photographs through Kappa coe cient calculation. Post-classi® cation comparison was found to be the most accurate procedure and presented the advantage of indicating the nature of the changes. Poor performances obtained by image enhancement procedures were attributed to the spectral variation due to di erences in soil moisture and in vegetation phenology between both scenes. Methods based on classi® cation were found to be less sensitive at these spectral variations and more robust when dealing with data captured at di erent times of the year
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