Observed features of a two-phase stellar wind from WR 136 in the vicinity of NGC 6888

A number of features are detected outside the nebula NGC 6888, within 1.2° (30 pc) of the star WR 136, which can be explained in a two-phase stellar-wind model. These include regions with fine filamentary gas structure that do not contain sources of stellar wind, extended radial “streams,” ultra-compact HII regions with high-velocity gas motions, and high-velocity gas motions outside the envelope of NGC 6888. The two-phase wind consists of a rarefied component and dense compact condensations, or “bullets.” The bullets generate cylindrical shocks in the interstellar gas, resulting in the presence of high-velocity gas up 20–30 pc from the star, outside the cavity formed by the rarified component of the wind.     

A model for superoutbursts in SU UMa-type binaries

We suggest a new mechanism for the superoutbursts in SU UMa binaries, in which the increase in the accretion rate resulting in a superoutburst is associated with the formation of a spiral “precessional” wave in the inner parts of the disk, where gas-dynamical perturbations are negligible. The existence of such waves was suggested by us previously. The results of three-dimensional gas-dynamical simulations have shown that a considerable increase in the accretion rate (by up to an order of magnitude) is associated with the formation of the precessional wave. The features of the precessional spiral wave can explain both the energy release in the superoutburst and all its observational manifestations. One distinguishing feature of superoutbursts in SU UMa-type stars is the formation of a “superhump” in the light curve. Our model reproduces well both the formation of a superhump and its observational features, including its period, which is up to 3–7% longer than the orbital period, and the detectability of the superhump independent of the orbital inclination of the binary.     

A furrow runs through it: An example of sustainable traditional irrigation in Western Cape Province,South Africa

Water and water related matters are important issues in water scarce countries like the Republic of South Africa. This is especially true for the agricultural sector that relies heavily on the availability of water for irrigation to ensure a secure food supply. In South Africa, present day irrigation projects rely on government subsidies and are usually large undertakings beyond the reach of individuals or small communities. The sustainability of such large irrigation projects is still a matter of debate. A 100 years ago a different set of rules applied. Irrigation could only be achieved by hand-dug furrows that supplied water in relatively small quantities to small farming communities. This paper investigated such a small community, the Leeukloof farming community in the Western Cape Province of the Republic of South Africa. For the past 93 years this community has maintained a furrow that supplies water not only to farms bordering the Perdeberg River, which supplies the furrow with water, but also to farms not bordering the river. The authors try to reconstruct the changes in agricultural practices brought about by the furrow, methods of water extraction during each phase, as well as the development and role of the furrow system. The perception by the community of the necessity of this method of water extraction from the river system is also investigated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Near-polar starspots and polar dynamo waves

A possible mechanism for the formation of near-polar magnetic spots on some stars with convective envelopes is proposed. The mechanism is based on the idea that the maximum of the dynamo waves that are excited in thin convective shells by the dynamo mechanism is shifted appreciably from the maximum of the magnetic-field sources in the direction of motion of the dynamo wave. If there is no region of super-rotation near the equator for some reason (as a consequence of disruption due to tidal interaction with a companion in a binary system, for example) and the wave of stellar activity propagates toward the poles rather than toward the equator, this maximum will be in the near-polar regions.     

Differential rotation and meridional circulation near the boundaries of the solar convection zone

Although the theory of differential rotation is in satisfactory agreement with helioseismological data for the deep convection zone, there are considerable discrepancies near the solar surface. This disagreement can be eliminated if the anisotropy of turbulent convection is taken into account together with the effects of nonuniformity of the medium, on which the most recent models for differential rotation are based. The model for the differential rotation of the convection envelope is supplemented by computations for the transition layer between nonuniform and rigid-body rotation in the upper layers of the solar radiative zone. These are the first computations of differential rotation for the entire volume of the Sun.     

A brief comparison of lava flows from the Deccan Volcanic Province and the Columbia-Oregon Plateau Flood Basalts: Implications for models of flood basalt emplacement

The nature and style of emplacement of Continental Flood Basalt (CFB) lava flows has been a matter of great interest as well as considerable controversy in the recent past. However, even a cursory review of published literature reveals that the Columbia River Basalt Group (CRBG) and Hawaiian volcanoes provide most of the data relevant to this topic. It is interesting to note, however, that the CRBG lava flows and their palaeotopographic control is atypical of other CFB provinces in the world. In this paper, we first present a short overview of important studies pertaining to the emplacement of flood basalt flows. We then briefly review the morphology of lava flows from the Deccan Volcanic Province (DVP) and the Columbia-Oregon Plateau flood basalts. The review underscores the existence of significant variations in lava flow morphology between different provinces, and even within the same province. It is quite likely that there were more than one way of emplacing the voluminous and extensive CFB lava flows. We argue that the establishment of general models of emplacement must be based on a comprehensive documentation of lava flow morphology from all CFB provinces.     

The environmental planning and management approach towards the development and management of the Osun natural spring project,Ibadan, Nigeria

There is a general shortage of potable water in Nigeria, partly through the lack of natural provision and partly because of rapid urban growth that has largely been unplanned. The paper describes the recent redevelopment of a public water facility in a run-down area of Ibadan which is part of the Sustainable Ibadan Project. Despite funding from national and international bodies, the development is strongly based at community level. The local inhabitants feel they have control over their own water supply through their representatives on the various planning and managing committees. This aims to reduce vandalism and to increase pride and involvement in the community. The project is a pilot for other projects around Ibadan, some of which have begun and others are being planned. This paper describes the administrative structures and management principles that have been employed. It forcefully advocates community-based planning and management which respects both the environment and the water-users, and involves a major “bottom-up” element. This revised version was published online in July 2006 with corrections to the Cover Date.     

Geochemistry and petrogenesis of anorogenic basic volcanic-plutonic rocks of the Kundal area,Malani Igneous Suite,western Rajasthan,India

The Kundal area of Malani Igneous Suite consists of volcano-plutonic rocks. Basalt flows and gabbro intrusives are associated with rhyolite. Both the basic rocks consist of similar mineralogy of plagioclase, clinopyroxene as essential and Fe-Ti oxides as accessories. Basalt displays sub-ophitic and glomeroporphyritic textures whereas gabbro exhibits sub-ophitic, porphyritic and intergrannular textures. They show comparable chemistry and are enriched in Fe, Ti and incompatible elements as compared to MORB/CFB. Samples are enriched in LREE and slightly depleted HREE patterns with least significant positive Eu anomalies. Petrographical study and petrogenetic modeling of [Mg]-[Fe], trace and REE suggest cogenetic origin of these basic rocks and they probably derived from Fe-enriched source with higher Fe/Mg ratio than primitive mantle source. Thus, it is concluded that the basic volcano-plutonic rocks of Kundal area are the result of a low to moderate degree (< 30%) partial melting of source similar to picrite/komatiitic composition. Within plate, anorogenic setting for the basic rocks of Kundal area is suggested, which is in conformity with the similar setting for Malani Igneous Suite.     

Topological model for the large solar flare of July 14, 2000

Using observational data obtained with the Yohkoh, SOHO, and TRACE satellites, it is shown that the three-dimensional structure of the large solar flare of July 14, 2000 was determined by the topology of the large-scale magnetic field of the active region giving rise to the flare. The locations and shapes of chromospheric ribbons and brightness centers on these ribbons are explained. The observed behavior of the flare is attributed to rapid magnetic reconnection in the corona. The electric field accelerating particles in the reconnecting current sheets is estimated.