A Model for the Sources of the Slow Solar Wind

Models for the origin of the slow solar wind must account for two seemingly contradictory observations: The slow wind has the composition of the closed field corona, implying that it originates from the continuous opening and closing of flux at the boundary between open and closed field. On the other hand, the slow wind also has large angular width, up to ~ 60{\circ}, suggesting that its source extends far from the open-closed boundary. We propose a model that can explain both observations. The key idea is that the source of the slow wind at the Sun is a network of narrow (possibly singular) open-field corridors that map to a web of separatrices and quasi-separatrix layers in the heliosphere. We compute analytically the topology of an open-field corridor and show that it produces a quasi-separatrix layer in the heliosphere that extends to angles far from the heliospheric current sheet. We then use an MHD code and MDI/SOHO observations of the photospheric magnetic field to calculate numerically, with high spatial resolution, the quasi-steady solar wind and magnetic field for a time period preceding the August 1, 2008 total solar eclipse. Our numerical results imply that, at least for this time period, a web of separatrices (which we term an S-web) forms with sufficient density and extent in the heliosphere to account for the observed properties of the slow wind. We discuss the implications of our S-web model for the structure and dynamics of the corona and heliosphere, and propose further tests of the model

Molecular and phenotypic characterisation of NS maize inbred lines.

Кукуруз је биљна врста која испољава велику фенотипску и генетичку варијабилност. У овом раду извршена је фенотипска и молекуларна карактеризација дивергентних инбред линија кукуруза које се користе у оплемењивачким програмима и које представљају могући извор алела са позитивним утицајем на агромонски важне особине. Такође, идентификовани су алели карактеристични за одређене хетеротичне групе и утврђене су потенцијално значајне везе између маркера и агрономски важних својстава применом асоцијативне анализе, са циљем даље примене у маркер асистираној селекцији. Анализирани материјал састојао се од 96 инбред линија из четири хетеротичне групе. Тридесет шест микросателитских маркера коришћено је за израчунавање параметара диверзитета генских локуса. Примењене су три кластер анализе на подацима добијеним молекуларном анализом. Пољски огледи су постављени у току две године, по потпуно случајном блок систему са три понављања. Дескриптивна статистика, анализа варијансе, линеарне корелације и анализа главних компоненти израчунате су за 13 особина. Везе између маркера и особина утврђене су применом општег и мешовитог линеарног модела. Просечан број алела износио је 8,3, просечна полиморфност појединачних локуса износила је 0,64, а проценат ретких алела 8,5% по локусу. Уочен је већи генетички диверзитет код BSSS него код Lancaster линија. Више од трећине алела било је карактеристично за само једну групу. Резултати кластер анализа су у великој мери били у међусобној сагласности. Анализа варијансе указала је на постојање статистички значајних разлика особина међу инбред линијама, годинама и локалитетима. Резултати кластер анализе фенотипских података били су у мањој мери сагласни са педигреима линија, него резулати анализе молекуларних података. Анализа главних компоненти издвојила је линије према хетеротичним групама и истакла њихове опште карактеристике. Велики број утврђених алела маркера са стабилним позитивним ефектима на принос указује на могући значај ових маркера у оплемењивању кукуруза.Maize has great phenotypic and genotypic variability. In this study a diverse set of maize inbred lines used in breeding programmes as a potential source of alleles with positive effects on important agronomic traits, was characterised at phenotypic and molecular level. Furthermore, alleles specific to heterotic groups were identified and potentially significant associations between markers and important agronomic traits which could be employed in marker assisted selection were determined. Ninety eight inbred lines from four heterotic groups were analysed. Thirty six microsatellite markers were used to obtain parameters for genetic diversity and three claster analyses were employed based on molecular data. The field trials were set in randomised block design with three replications during two years to acquire phenotypic data. Descriptive statistics, analysis of variance, linear correlations and principal component analysis were performed for 13 traits. The associations between markers and traits were identified by the application of general and mixed linear model. The average number of alleles was 8,3, the average value of polymorphism information content was 0,64, whereas the percentage of rare alleles was 8,5%. Greater genetic diversity of BSSS inbred lines compared to the lines from Lancaster group were observed. More than one third of alleles were specific to only one of these two groups. The results of cluster analyses were to a large extent in agreement with each other. Analysis of variance indicated statistically significant differences in traits among inbred lines, years and locations. Cluster analysis based on phenotypic data was in less consistent with pedigrees of the inbred lines than the cluster analysis based on molecular data. Principal component analysis grouped inbreds into heterotic groups and indicated their general characteristics. A large number of identified marker alleles with stable positive effects on grain yield suggested the potential importance of these markers in maiz

Genetic Variability in Different Lucerne (\u3cem\u3eMedicago Sativa\u3c/em\u3e) Genotypes

One of the basic goals of modern lucerne breeding programmes is creation of new cultivars with a great potential for high quality and stable yields of both forage and hay (Riday & Brummer, 2002). Such cultivars meet increased needs of animal husbandry and must contribute to diverse farming systems (Luki , 2000). Our trial was aimed at determining genetic variability of yield components in 7 lucerne genotypes, as well as at evaluation of their breeding potential as gene donors to new lucerne cultivar

Evidence for topological nonequilibrium in magnetic configurations

We use direct numerical simulations to study the evolution, or relaxation, of magnetic configurations to an equilibrium state. We use the full single-fluid equations of motion for a magnetized, non-resistive, but viscous fluid; and a Lagrangian approach is used to obtain exact solutions for the magnetic field. As a result, the topology of the magnetic field remains unchanged, which makes it possible to study the case of topological nonequilibrium. We find two cases for which such nonequilibrium appears, indicating that these configurations may develop singular current sheets.Comment: 10 pages, 5 figure

Nonlinear force-free magnetic field extrapolations: comparison of the Grad-Rubin and Wheatland-Sturrock-Roumeliotis algorithm

We compare the performance of two alternative algorithms which aim to construct a force-free magnetic field given suitable boundary conditions. For this comparison, we have implemented both algorithms on the same finite element grid which uses Whitney forms to describe the fields within the grid cells. The additional use of conjugate gradient and multigrid iterations result in quite effective codes. The Grad-Rubin and Wheatland-Sturrock-Roumeliotis algorithms both perform well for the reconstruction of a known analytic force-free field. For more arbitrary boundary conditions the Wheatland-Sturrock-Roumeliotis approach has some difficulties because it requires overdetermined boundary information which may include inconsistencies. The Grad-Rubin code on the other hand loses convergence for strong current densities. For the example we have investigated, however, the maximum possible current density seems to be not far from the limit beyond which a force free field cannot exist anymore for a given normal magnetic field intensity on the boundary.Comment: 21 pages, 13 figure

3D Coronal Density Reconstruction and Retrieving the Magnetic Field Structure during Solar Minimum

Measurement of the coronal magnetic field is a crucial ingredient in understanding the nature of solar coronal phenomena at all scales. We employed STEREO/COR1 data obtained during a deep minimum of solar activity in February 2008 (Carrington rotation CR 2066) to retrieve and analyze the three-dimensional (3D) coronal electron density in the range of heights from 1.5 to 4 Rsun using a tomography method. With this, we qualitatively deduced structures of the coronal magnetic field. The 3D electron density analysis is complemented by the 3D STEREO/EUVI emissivity in the 195 A band obtained by tomography for the same CR. A global 3D MHD model of the solar corona was used to relate the reconstructed 3D density and emissivity to open/closed magnetic field structures. We show that the density maximum locations can serve as an indicator of current sheet position, while the locations of the density gradient maximum can be a reliable indicator of coronal hole boundaries. We find that the magnetic field configuration during CR 2066 has a tendency to become radially open at heliocentric distances greater than 2.5 Rsun. We also find that the potential field model with a fixed source surface (PFSS) is inconsistent with the boundaries between the regions with open and closed magnetic field structures. This indicates that the assumption of the potential nature of the coronal global magnetic field is not satisfied even during the deep solar minimum. Results of our 3D density reconstruction will help to constrain solar coronal field models and test the accuracy of the magnetic field approximations for coronal modeling.Comment: Published in "Solar Physics

Structure and Dynamics of the Sun's Open Magnetic Field

The solar magnetic field is the primary agent that drives solar activity and couples the Sun to the Heliosphere. Although the details of this coupling depend on the quantitative properties of the field, many important aspects of the corona - solar wind connection can be understood by considering only the general topological properties of those regions on the Sun where the field extends from the photosphere out to interplanetary space, the so-called open field regions that are usually observed as coronal holes. From the simple assumptions that underlie the standard quasi-steady corona-wind theoretical models, and that are likely to hold for the Sun, as well, we derive two conjectures on the possible structure and dynamics of coronal holes: (1) Coronal holes are unique in that every unipolar region on the photosphere can contain at most one coronal hole. (2) Coronal holes of nested polarity regions must themselves be nested. Magnetic reconnection plays the central role in enforcing these constraints on the field topology. From these conjectures we derive additional properties for the topology of open field regions, and propose several observational predictions for both the slowly varying and transient corona/solar wind.Comment: 26 pages, 6 figure

Slip-Squashing Factors as a Measure of Three-Dimensional Magnetic Reconnection

A general method for describing magnetic reconnection in arbitrary three-dimensional magnetic configurations is proposed. The method is based on the field-line mapping technique previously used only for the analysis of magnetic structure at a given time. This technique is extended here so as to analyze the evolution of magnetic structure. Such a generalization is made with the help of new dimensionless quantities called "slip-squashing factors". Their large values define the surfaces that border the reconnected or to-be-reconnected magnetic flux tubes for a given period of time during the magnetic evolution. The proposed method is universal, since it assumes only that the time sequence of evolving magnetic field and the tangential boundary flows are known. The application of the method is illustrated for simple examples, one of which was considered previously by Hesse and coworkers in the framework of the general magnetic reconnection theory. The examples help us to compare these two approaches; they reveal also that, just as for magnetic null points, hyperbolic and cusp minimum points of a magnetic field may serve as favorable sites for magnetic reconnection. The new method admits a straightforward numerical implementation and provides a powerful tool for the diagnostics of magnetic reconnection in numerical models of solar-flare-like phenomena in space and laboratory plasmas.Comment: 39 pages, 9 figures, corrected typos, to appear in ApJ, March 200