Low-resolution spectra of the Io plasma torus 2 days after the Ulysses encounter

Low-resolution spectra of the Io plasma torus have been obtained on 10 and 11 February 1992 (2 days after the Ulysses encounter) using the 2 m telescope of the Bulgarian National Observatory. The spectra show the forbidden line emissions of S⁺ (λλ 6716, 6731 Å) and S²⁺ (λ 6312 Å). Measured intensities are compared with a Voyager-type model. The intensity distribution of [SII] is found to deviate from the model predictions which indicates a change in the torus at the Ulysses encounter when compared with the Voyager epoch. A corotating structure was observed, both in [SII] and [SIII], at λ_III = 170°, showing that the torus was not azimuthally symmetric. The λ 6716/λ 6731 and λ 6731/ λ 6312 line ratios indicate a higher electron density at the time of the Ulysses observations. Additionally, the shift of the torus caused by the dawn-dusk electric field could be observed. Peak intensities in [SII] were found at 5.66 ± 0.02 R_J on the West ansa and 5.91 ± 0.04 R_J on the East.     

Low resolution spectroscopy of selected Algol systems

The analysis of spectroscopic data for 30 Algol-type binaries is presented. All these systems are short period Algols having primaries with spectral types B and A. Dominant spectral lines were identified for the spectra collected and their equivalent widths were calculated. All the spectra were examined to understand presence of mass transfer, a disk or circumstellar matter and chromospheric emission. We also present first spectroscopic and period study for few Algols and conclude that high resolution spectra within and outside the primary minimum are needed for better understanding of these Algol type close binaries.     

Relation of the observed far ultraviolet solar irradiance to the solar magnetic sector structure

Comparison of the observed solar far ultraviolet irradiance and the observed solar sector structure during 1969 through 1972 shows a tendency for EUV maxima to be located near sector boundaries.     

Influence of shallow infiltration on time-lapse ERT: Experience of advanced interpretation

Previous time-lapse Electrical Resistivity Tomography (ERT) studies have experienced difficulties in reconstructing reliable calculated resistivity changes in the subsurface. Increases or decreases of resistivity appear in the calculated ERT image where no changes were noted in the subsurface, leading to erroneous hydrological interpretations of the geophysical results. In this article, we investigate how a variation of actual resistivity with time and at shallow depth can influence time-lapse ERT results and produce resistivity artefacts at depth. We use 1 and 2-D numerical modelling to simulate infiltration scenarios. Using a standard time-lapse inversion, we demonstrate the resistivity artefact production according to the electrode spacing parameter. We used an advanced inversion methodology with a decoupling line at shallow depth to attenuate or remove resistivity artefacts. We also applied this methodology to a field data set obtained in a semi-arid environment in Burkina Faso, West Africa. Here, time-lapse ERT shows several resistivity artefacts of calculated resistivity if a standard inversion is used. We demonstrate the importance of a dense sampling of shallow resistivity variations at shallow depth. Advanced interpretation allows us to significantly attenuate or remove the resistivity artefact production at intermediate depth and produce reliable interpretation of hydrological processes.     

Graded-Density Reservoirs for Accessing High Stress Low Temperature Material States

In recently developed laser-driven shockless compression experiments an ablatively driven shock in a primary target is transformed into a ramp compression wave in a secondary target via unloading followed by stagnation across an intermediate vacuum gap. Current limitations on the achievable peak longitudinal stresses are limited by the ability of shaping the temporal profile of the ramp compression pulse. We report on new techniques using graded density reservoirs for shaping the loading profile and extending these techniques to high peak pressures.     

Exact physical Maxwell-Einstein Tolman-VII solution and its use in stellar models

We derive an exact Maxwell-Einstein metric for a spherically symmetric static perfect fluid with mass and charge (Q), that electrifies the Tolman-VII metric and meets applicable physical boundary conditions. We show that there is more than one way to electrify any Q=0 metric, depending on whether metric component g _tt , g _rr , or neither, is independent of Q. We illustrate an approach not yet in the literature in which g _rr is independent of Q. When applied to a baryonic stellar model, this metric is versatile, capable of producing a range of values for radius, mass, Q, and far-field mass due to the presence of charge.     

Small-scale auroral arc distortions

Small-scale spatially periodic distortions of auroral forms have been studied utilizing low-light level television observations made at various locations in the Northern and Southern Hemispheres. The most commonly observed features were folds and vortex-like curl formations. The curls, identified here with the Kelvin-Helmholtz instability due to fluid shear, invariably had a counterclockwise rotational shape and motion when viewed in a direction anti-parallel to the Earth's magnetic field. The typical measured wavelength (5 km) and measured growth rate (4.2 sec⁻¹) were used to evaluate the Kelvin-Helmholtz dispersion relation for the apparent shear ω_s = ∂ ν_x/ ∂y (28 sec⁻¹). The apparent horizontal velocities of both folds (0–5 km/sec) and curls (0–22 km/sec) were invariably observed to be counterclockwise with respect to the multiple arc centre when viewed antiparallel to B. Consistent agreement between rotational shape and rotational motion suggests that the apparent growth rate and the apparent horizontal velocities closely approximate the actual values. If the shear results from E×B drifts in a space charge field, the calculated value for ω_s, implies an unneutralized electron density 0–1 cm⁻³ and a ΔE across the arc element 500mV/m. The velocity measurements indicate that the ΔE values for individual elements can combine to produce transient electric fields at the edges of multiple arcs as high as 1000 mV/m.     

Origin of magmatic sulfides in a Proterozoic island arc—an example from the Portneuf–Mauricie Domain,Grenville Province,Canada

The Portneuf–Mauricie Domain (PMD), located in the south-central part of the Grenville province, contains Mesoproterozoic Ni–Cu ± platinum-group element (PGE) prospects hosted in a variety of plutonic intrusions (layered, with simple structures, or zoned) and emplaced in a mature island arc setting. A two-stage model is envisaged to explain the formation of magmatic sulfides. An early loss of a small amount of sulfides in the conduits of primitive, hydrous mantle-derived melts under high fO₂, resulted in depletion of the magmas in chalcophile and precious metals (Cu/Pd ratios vary from initial mantle values up to 1.6 × 10⁶). Then, nearer the mineralized zones, the magmas interacted with sulfide-bearing country rocks, resulting in felsification of the magmas, assimilation of crustal sulfur (δ ³⁴S values up to +5.5‰), and the formation of an immiscible sulfide liquid. Liquid-sulfide formation was followed by variable interactions between the silicate and sulfide magmas, which were responsible for the enrichment of sulfides in Ni, Cu, and, locally, PGE. Indeed, low R factors are found for prospects hosted in intrusions with a simple internal structure and in layered intrusions whereas high R factors are found for prospects hosted in zoned intrusions. Finally, sulfide melt may have been partly incorporated into later pulses of magma and injected into shallow magma chambers to form the PMD prospects. The PMD prospects share common characteristics with other well-known deposits (Aguablanca, Vammala, Stormyrplunen, and deposits in Alaskan/Ural-type intrusions), attesting to the Ni, Cu, and PGE potential of deposits associated with subduction-zone settings.     

Morphological similarities between DBM and a microeconomic model of sprawl

We present a model that simulates the growth of a metropolitan area on a 2D lattice. The model is dynamic and based on microeconomics. Households show preferences for nearby open spaces and neighbourhood density. They compete on the land market. They travel along a road network to access the CBD. A planner ensures the connectedness and maintenance of the road network. The spatial pattern of houses, green spaces and road network self-organises, emerging from agents individualistic decisions. We perform several simulations and vary residential preferences. Our results show morphologies and transition phases that are similar to Dieletric Breakdown Models (DBM). Such similarities were observed earlier by other authors, but we show here that it can be deducted from the functioning of the land market and thus explicitly connected to urban economic theory.