Experimental Identification of the Kink Instability as a Poloidal Flux Amplification Mechanism for Coaxial Gun Spheromak Formation

The magnetohydrodynamic kink instability is observed and identified experimentally as a poloidal flux amplification mechanism for coaxial gun spheromak formation. Plasmas in this experiment fall into three distinct regimes which depend on the peak gun current to magnetic flux ratio, with (I) low values resulting in a straight plasma column with helical magnetic field, (II) intermediate values leading to kinking of the column axis, and (III) high values leading immediately to a detached plasma. Onset of column kinking agrees quantitatively with the Kruskal-Shafranov limit, and the kink acts as a dynamo which converts toroidal to poloidal flux. Regime II clearly leads to both poloidal flux amplification and the development of a spheromak configuration.Comment: accepted for publication in Physical Review Letter

On O-X mode conversion in 2D inhomogeneous plasma with a sheared magnetic field

The conversion of an ordinary wave to an extraordinary wave in a 2D inhomogeneous slab model of the plasma confined by a sheared magnetic field is studied analytically.Comment: sub. to PPC

Observational properties of a kink unstable coronal loop

Aims. Previous work on the dynamics of the kink instability has concentrated on the evolution of the magnetic field and associated current sheets. Here we aim to determine the observational consequences of the kink instability in short coronal loops, particularly what images TRACE would record of such an instability. This paper concentrates on the internal m = 1 mode where the kink structure of the instability may not be apparent from the global field shape. This is most relevant to the observation of active region brightenings and coronal bright points. Methods. An existing fluid code was modified to include the TRACE temperature response function in order to calculate temporally and spatially averaged, line of sight images in the 171, 195 and 284 Å band passes for straight, kink unstable flux tubes. Results. Two new fluid effects of the kink instability are discovered: the circular enhancement of the density at the foot points and the appearance of a low density band running across the flux tube. The second of these effects is shown to be imagable by TRACE and hence would be a good candidate observational signature for an internal m = 1 kink unstable loop

Observation of kink instability during small B5.0 solar flare on 04 June, 2007

Using multi-wavelength observations of SoHO/MDI, SOT-Hinode/blue-continuum (4504 \AA), G-band (4305 \AA), Ca II H (3968 \AA) and TRACE 171 \AA, we present the observational signature of highly twisted magnetic loop in AR 10960 during the period 04:43 UT-04:52 UT at 4 June, 2007. SOT-Hinode/blue-continuum (4504 \AA) observations show that penumbral filaments of positive polarity sunspot have counter-clock wise twist, which may be caused by the clock-wise rotation of the spot umbrae. The coronal loop, whose one footpoint is anchored in this sunspot, shows strong right-handed twist in chromospheric SOT-Hinode/Ca II H (3968 \AA) and coronal TRACE 171 \AA\, images. The length and the radius of the loop are $L\sim$80 Mm and $a\sim$4.0 Mm respectively. The distance between neighboring turns of magnetic field lines (i.e. pitch) is estimated as $\approx$ 10 Mm. The total twist angle, $\Phi\sim$12$\pi$ (estimated for the homogeneous distribution of the twist along the loop), is much larger than the Kruskal -Shafranov instability criterion. We detected clear double structure of the loop top during 04:47-04:51 UT on TRACE 171 \AA \ images, which is consistent with simulated kink instability in curved coronal loops (T{\"o}r{\"o}k et al. 2004). We suggest, that the kink instability of this twisted magnetic loop triggered B5.0 class solar flare, which occurred between 04:40 UT and 04:51 UT in this active region.Comment: 24 pages, 5 Figures; The Astrophysical Journa

Nuevos datos sobre la distribución y la biología reproductiva de Canthon imitator Brown 1946 (Coleoptera: Scarabaeidae: Scarabaeinae)

Canthon imitator Brown 1946 is registered for the first time in the Municipality of Papantla, Veracruz, Mexico. It is a roller, diurnal, coprophagous dung beetle, abundant in the collection site from May to July. The females have only the left ovary with one ovariola. A female oviposits a single egg every 4 to 5 days in a piriform nest ball. Males have two testicles with six spherical testicular follicles. The development to imago lasts approximately 30 days, as in the other Canthon species that have already been studied.Canthon imitator Brown 1946 se registra por primera vez en el Municipio de Papantla, Veracruz, México. Este es el registro más meridional que se tiene de esta especie. Es un escarabajo estercolero rodador, diurno, abundante en el sitio de colecta de mayo a julio. Las hembras tienen sólo el ovario izquierdo con una ovariola. Ovipositan un solo huevo cada 4 a 5 días en una bola nido piriforme. Los machos tienen dos testículos, cada uno con seis folículos testiculares esféricos. El desarrollo hasta imago dura aproximadamente 30 días como en otras especies de Canthon estudiadas

On handling urban informality in southern Africa

In this article I reconsider the handling of urban informality by urban planning and management systems in southern Africa. I argue that authorities have a fetish about formality and that this is fuelled by an obsession with urban modernity. I stress that the desired city, largely inspired by Western notions of modernity, has not been and cannot be realized. Using illustrative cases of top–down interventions, I highlight and interrogate three strategies that authorities have deployed to handle informality in an effort to create or defend the modern city. I suggest that the fetish is built upon a desire for an urban modernity based on a concept of formal order that the authorities believe cannot coexist with the “disorder” and spatial “unruliness” of informality. I question the authorities' conviction that informality is an abomination that needs to be “converted”, dislocated or annihilated. I conclude that the very configuration of urban governance and socio-economic systems in the region, like the rest of sub-Saharan Africa, renders informality inevitable and its eradication impossible