The Magnetic Field in the Solar Atmosphere

This publication provides an overview of magnetic fields in the solar atmosphere with the focus lying on the corona. The solar magnetic field couples the solar interior with the visible surface of the Sun and with its atmosphere. It is also responsible for all solar activity in its numerous manifestations. Thus, dynamic phenomena such as coronal mass ejections and flares are magnetically driven. In addition, the field also plays a crucial role in heating the solar chromosphere and corona as well as in accelerating the solar wind. Our main emphasis is the magnetic field in the upper solar atmosphere so that photospheric and chromospheric magnetic structures are mainly discussed where relevant for higher solar layers. Also, the discussion of the solar atmosphere and activity is limited to those topics of direct relevance to the magnetic field. After giving a brief overview about the solar magnetic field in general and its global structure, we discuss in more detail the magnetic field in active regions, the quiet Sun and coronal holes.Comment: 109 pages, 30 Figures, to be published in A&AR

Interaction of a Moreton/EIT wave and a coronal hole

We report high-cadence H-alpha observations of a distinct Moreton wave observed at Kanzelhoehe Solar Observatory associated with the 3B/X3.8 flare and CME event of 2005 January 17. The Moreton wave can be identified in about 40 H-alpha frames over a period of 7 min. The EIT wave is observed in only one frame but the derived propagation distance is close to that of the simultaneously measured Moreton wave fronts indicating that they are closely associated phenomena. The large angular extent of the Moreton wave allows us to study the wave kinematics in different propagation directions with respect to the location of a polar coronal hole (CH). In particular we find that the wave segment whose propagation direction is perpendicular to the CH boundary (``frontal encounter'') is stopped by the CH which is in accordance with observations reported from EIT waves (Thompson et al. 1998). However, we also find that at a tongue-shaped edge of the coronal hole, where the front orientation is perpendicular to the CH boundary (the wave ``slides along'' the boundary), the wave signatures can be found up to 100 Mm inside the CH. These findings are briefly discussed in the frame of recent modeling results.Comment: 14 pages, 6 figures, accepted for publication in the Ap

Small Open Reading Frames, Non-Coding RNAs and Repetitive Elements in Bradyrhizobium japonicum USDA 110

Small open reading frames (sORFs) and genes for non-coding RNAs are poorly investigated components of most genomes. Our analysis of 1391 ORFs recently annotated in the soybean symbiont Bradyrhizobium japonicum USDA 110 revealed that 78% of them contain less than 80 codons. Twenty-one of these sORFs are conserved in or outside Alphaproteobacteria and most of them are similar to genes found in transposable elements, in line with their broad distribution. Stabilizing selection was demonstrated for sORFs with proteomic evidence and bll1319_ISGA which is conserved at the nucleotide level in 16 alphaproteobacterial species, 79 species from other taxa and 49 other Proteobacteria. Further we used Northern blot hybridization to validate ten small RNAs (BjsR1 to BjsR10) belonging to new RNA families. We found that BjsR1 and BjsR3 have homologs outside the genus Bradyrhizobium, and BjsR5, BjsR6, BjsR7, and BjsR10 have up to four imperfect copies in Bradyrhizobium genomes. BjsR8, BjsR9, and BjsR10 are present exclusively in nodules, while the other sRNAs are also expressed in liquid cultures. We also found that the level of BjsR4 decreases after exposure to tellurite and iron, and this down-regulation contributes to survival under high iron conditions. Analysis of additional small RNAs overlapping with 3’-UTRs revealed two new repetitive elements named Br-REP1 and Br-REP2. These REP elements may play roles in the genomic plasticity and gene regulation and could be useful for strain identification by PCR-fingerprinting. Furthermore, we studied two potential toxin genes in the symbiotic island and confirmed toxicity of the yhaV homolog bll1687 but not of the newly annotated higB homolog blr0229_ISGA in E. coli. Finally, we revealed transcription interference resulting in an antisense RNA complementary to blr1853, a gene induced in symbiosis. The presented results expand our knowledge on sORFs, non-coding RNAs and repetitive elements in B. japonicum and related bacteria

Depth map from the combination of matched points with active contours

IEEE Intelligent Vehicles Symposium (IVS), 2000, Dearborn (EE.UU.)This paper describes the analysis of an active contour fitted to a target in a sequence of images recorded by a freely moving uncalibrated camera. The motivating application is the visual guidance of a robot towards a target. Contour deformations are analysed to extract the scaled depth of the target, and to explore the feasibility of 3D egomotion recovery. The scaled depth is used to compute the time to contact, which provides a measure of distance to the target, and also to improve the common depth maps obtained from point matches, which are a valuable input for the robot to avoid obstacles.This work was supported by the project 'Navegación basada en visión de robots autónomos en entornos no estructurados.' (070-724).Peer Reviewe

Pyrolysis/methylation of soil fulvic acids: benzenecarboxyllc acids revisited

4 páginas, 1 figura, 3 tablas, 20 referencias.Fulvic acid (FA) is, perhaps, the most complex fraction of soil humic substances due to its extremely variable composition depending on the nature of the environment (1) and the isolation method (2). Practically all available techniques and methods have been applied to FAs (3), in order to understand their chemical structure, but in spite of extensive studies, their nature is still a matter of debate. Chemical degradations have been widely used to characterize FAs in terms of structural units. However, they provide only partial information on the molecular constituents. For instance, acid hydrolysis reveals the presence of sugars and some phenols, while oxidations yield alkanes, fatty acids, phenolic acids, and benzenecarboxylic acids (4). Benzenecarboxylic acids were considered the building blocks of the humic molecule in the 19709, and on the basis of permanganate oxidations and other analyses, Schnitzer and Khan (4) proposed a model made up of phenolic and benzenecarboxylic acids held together by hydrogen bonds, which were suggested to account for a significant part of the FA structure.Peer reviewe