Improved theoretical line ratios for Ciii in the Sun

The recent twelve-state R-matrix calculations of electron excitation rates in Ciii by Berrington are used to derive level populations applicable to the solar transition region. Line ratios R = I(2p ^{2 3} P ^e - 2s2p ³ P ^°)/I(2s2p ¹ P ^° - 2s ^{2 1} S ^e ) and R ₂=I(2p ^{2 1} S ^e - 2s2p ¹ P ^°)/I(2p ^{2 3} P ^e - 2s2p ³ P ^°) deduced from these data in conjunction with the relevent transition probabilities are found to be in much better agreement with the observed quiet Sun values than those determined from the level population calculations of Keenan et al.     

Thermal imbalance effects on pulsational stability in stellar models

The treatment followed by Coxet al. (1973) for the estimation of the effects of thermal imbalance on the pulsational stability of stars is applied to Roche and point source (Chandrika Prashad) model. The calculations suggest that the eigenvalues obtained for the above model are correct to 0(t _ff/t_s). The expressions for stability coefficients and corresponding eigenfunctions for the stars in thermal imbalance for the above models have also been derived.     

Accumulation of Zn,Cu and Cd by crabs and barnacles

The crab Carcinus maenas (L.) and the barnacle Elminius modestus Darwin were exposed to a range of dissolved concentrations of Zn, Cu and Cd for 21 days in artificial seawater. Accumulation of Zn and Cu by crabs has been interpreted in terms of the presence of a regulation mechanism to maintain constant body concentrations (83·2 ± 19·4 μg Zn g^?1 dry wt.; 39·8 ± 9·8 μg Cu g^?1 dry wt.) under varying external dissolved metal levels, until a threshold dissolved metal concentration (c. 400 μg Zn l^?1; c. 170 μg Cu l^?1) beyond which net accumulation of metal begins. Cadium appears to be accumulated by C. maenas at all exposures with no evidence for regulation of body cadmium concentrations. Exposure of E. modestus to Zn, Cu or Cd caused net accumulation of the respective metal in the bodies of the barnacles, with no evidence for regulation of body metal concentrations.     

On the structure of the Ivrea-Verbano Zone (northern Italy) and its implications for present-day lower continental crust geometry

The Ivrea-Verbano Zone in northern Italy represents a section through the lower continental crust which has been tilted and emplaced into its present position during the Alpine orogeny. Recent and on-going structurally-oriented geological mapping in this region is providing new information about the geometry of the complex. The central part of the zone is dominated by a large basic complex (the 'mafic formation') which is intrusive into the surrounding gneisses. The foliation within the envelope of gneisses is deflected around the intrusive complex as if by ballooning, but in the region south-west of Monte Capio both units are folded together into a tight to isoclinal steeply plunging fold with an amplitude of c. 10 km. This fold locally inverts the stratigraphy of the layered basic group of the complex, and is thought to be the result of gravitational collapse following intrusion and inflation of a large magma body into the lower crust.
Several high-temperature shear zones have now been traced within the country rock for distances up to 20 km. The geometry of these, and their relationship to the basic complex suggests that at least some of the extensional collapse of the mafic body is related to uplift caused by intrusion of this body.
Close parallels can be drawn between the observed structure in the Ivrea-Verbano Zone (after removing the effects of late, low-temperature faulting and folding related to emplacement of the rocks into their present position), and those inferred from deep seismic reflection profiling in areas of current extension such as parts of the US Basin and Range province.     

Spectral variations of DY Cen

Two high resolution spectra of the hot RCrB star DY Cen in the red region are compared. The photospheric absorption lines show a radial velocity variation of 12 kms-1 between 1989 July and 1992 May. Emission components to some CII lines present in 1989 are almost entirely absent in 1992. Nebular forbidden lines of [OI], [NII] and [SII] appear unchanged from 1989 to 1992     

Rayleigh-Taylor instability of a plasma with finite ion Larmor radius effects

The stability of an infinitely conducting plasma of variable density has been investigated taking into account the finiteness of the ion Larmor radius. The perturbations propagating along the ambient magnetic field are considered. It is established that, in general,n ² is necessarily real, wheren is the growth rate of disturbance, thus ruling out the possibility of overstability or damped oscillations. The solution is shown to be characterized by a variational principle, which provides the basis for obtaining an approximate solution of the problem. Two density distributions are considered: (i) a continuously stratified plasma layer and (ii) two semi-infinitely extending plasmas of constant densities separated by a horizontal interface. In both cases it has been shown that for the said disturbances the stability criterion remains unaffected by the inclusion of finite Larmor radius effects, though the amplified motion is strongly inhibited due to their inclusion.     

Analytical and numerical analysis of the generalized Shkarofsky function

The main analytical properties of the generalized Shkarofsky function and a numerical code for its computation are discussed. The results of a numerical analysis are compared with the results of an asymptotic analysis for parameter values relevant to the problem of whistler-mode propagation in the Earth's magnetosphere. This comparison allows us to specify the range of applicability of different approximations to the generalized Shkarofsky function, which have been used for the analysis of relativistic effects on whistler-mode propagation and instability.     

Experimental simulation of Titan's atmosphere: Detection of ammonia and ethylene oxide

For several years now, an experimental simulation of Titan's atmosphere has been on going at LISA. A cold plasma is established in a gas mixture representative of the atmosphere of the satellite. In these experiments, more than 70 organic compounds have been identified, including the first identification in this type of experimental simulation of C₄N₂ already detected in its solid form on Titan, which suggests that the setup correctly mimics the chemistry of Titan's atmosphere.We have carried out the first experimental simulation including O-containing compounds in order to study the influence of the presence of CO on the chemical behavior of Titan's atmosphere. With the help of gas chromatography–mass spectrometry (GC–MS) and infrared spectroscopy (IRS) we can thus determine which minor species still undetected in Titan's atmosphere are likely to be present and understand the complex chemistry of the atmosphere of this satellite. Surprisingly we have identified unpredicted O-containing gaseous compounds, mainly ethylene oxide (also named oxirane, C₂H₄O). This molecule has been observed in the interstellar medium by observation in the millimeter region (Astrophys. J. 489 (1997) 553; Astron. Astrophys. 337 (1998) 275). On the contrary, the predicted O-compounds (formaldehyde and methanol) have not been identified in this experiment. Furthermore, we have identified NH₃ in the gaseous products with an initial mixture of N₂ (98%) and CH₄ (2%).The paper describes the experimental device used in this work, in particular the IRS and GC–MS techniques. We also comment the results related to the detection of the O-containing compounds and NH₃ and their implications on our knowledge of the chemistry of Titan's atmosphere and on the retrieval of the future Titan data expected from Cassini-Huygens.