Finite Larmor radius effects on the Rayleigh-Taylor instability of a rotating plasma of variable density

The Rayleigh-Taylor instability in a rotating plasma of variable density has been investigated to include simultaneously the effects of viscosity and the finiteness of the ion Larmor radius. It is shown that, for a plasma in which the density is stratified along the vertical, the solution is characterized by a variational principle. Making use of this, proper solutions have been otained for a semiinfinite plasma in which the density varies exponentially. The dispersion relation has been solved numerically and it is found that the influence of the effects of both FLR and viscosity is stabilizing. The Coriolis forces are found to have a dual role, stabilizing for small wave numbers and destabilizing for large wave numbers. The range of the small wave numbers, over which the Coriolis forces have a stabilizing influence, is found to increase with Coriolis forces.     

Source,transport and deposition of atmospheric phosphorus over the Northwestern Mediterranean

Atmospheric concentrations and total deposition (wet+dry) of phosphorus were measured over the northwestern Mediterranean between april 1985 and march 1988. A seasonal cycle of both atmospheric concentrations and total deposition is observed, the higher values being recorded during the dry season. Air-mass trajectory analyses allow an identification of the major sources of atmospheric phosphorus: soil-derived dust from desert areas of north Africa and anthropogenic emissions from european countries. The impact of the atmospheric input as a source of phosphorus for surface Mediterrancan waters is tentatively assessed on both annual and seasonal time scales. The results suggest that the atmospheric input of phosphorus could be significant to Mediterranean oligotrophic zones, especially during summer when phosphorus input from deeper waters into the photic layer is minimum.     

Tritium-Verteilung,Durchmischungsverhältnisse und Altersstruktur der Wassermasse im Vierwaldstättersee

Tritium of thermonuclear origin was measured in four different depth profiles in the Lake of Lucerne. Its concentration distribution yielded information on the mixing within the water mass under observation. A simple model was established for approximating the age structure of the water layers.     

Die Zielsetzung einer allgemeinen quantitaiven Methode in der Gravimetrie

Summary After introduction in 1. and definitions in 2.A. the separately well known or evident relations representing the fundamental problems of the interpretation in the gravity are perpicuously summarised in 2.b. by means of the group theory. From the the following conclusions can be drawn (in 2.C.): 1.) from the point of view of the quantitative interpretation all gravity-maps are totally equivalent in respect of both their ambiguity and the informations that they are able to give, 2.) the quantity of the informations obtained from the gravity maps is growing withthe increasing number of other informations and with greater accuracy of the measurements. Therefore the development of a general quantitative method is proposed (with concrete points of views), to realise the theoretical possibilities.-In 3.) some problems of the derivative maps are discused in connection with the foregoings.     

Chuaria circularis from the early Mesoproterozoic Suket Shale, Vindhyan Supergroup, India: Insights from light and electron microscopy and pyrolysis-gas chromatography

Chuaria circularis (Walcott 1899) from the Suket Shale of the Vindhyan Supergroup (central India) has been reinvestigated for its morphology and chemical composition using biostatistics, electron microscopy and pyrolysis-gas chromatography. Morphology and microscopic investigations provide little clues on the specific biological affinity ofChuaria as numerous preservational artifacts seem to be incorporated. On the contrary, the predominance of η aliphatic pyrolysates of presently studiedChuaria from India rather supports an algal affinity. Moreover, the reflectance ofC circularis can be used to obtain a comparative maturity parameter of the Precambrian sediments. The review of the age and geographical distribution ofC circularis constrains that this species cannot be considered as an index fossil for the Proterozoic time.     

Geomagnetic excursion in the late Cretaceous

Summary. Two sedimentary cores from the western Pacific display a palaeo-magnetic record of the late Cretaceous long normal interval and the boundary reversed interval corresponding to seafloor spreading anomalies 33–34. Near the young end of this reversed interval, a systematic excursion of inclinations is observed in both cores. Samples are very stable to both alternating field and thermal demagnetization. Blocking temperatures and Curie points suggest that the remanence is carried primarily by magnetite, but with an additional contribution from hematite. Approximate sedimentation rates derived from biostratigraphy suggest that the excursion had a duration of between 46 000 and 54 000yr and occurred about 236000–303000 yr before the succeeding polarity reversal. The excursion, thus, may represent an aborted geomagnetic field reversal.     

Mössbauer and molecular orbital study of chlorites

The different Fe²⁺ lattice sites in iron-rich chlorites have been characterized by Mössbauer spectroscopy and molecular orbital calculations in local density approximation. The Mössbauer measurements were recorded at 77?K within a small velocity range (±3.5?mm?s^?1) to provide high energy resolution. Additionally, measurements were recorded in a wider velocity range (±10.5?mm?s^?1) at temperatures of 140, 200, and 250?K in an applied field (7?T) parallel to the γ-beam. The zero-field spectra were analyzed with discrete Lorentzian-shaped quadrupole doublets to account for the Fe²⁺ sites M1, M2, and M3 and with a quadrupole distribution for Fe³⁺ sites. Such a procedure is justified by the results obtained from MO calculations, which reveal that different anion (OH^?) distributions in the first coordination sphere of M1, M2, and M3 positions have more influence on the Fe²⁺ quadrupole splitting than cationic disorder. The spectra recorded in applied field were analyzed in the spin-Hamiltonian approximation, yielding a negative sign for the electric field gradient (efg) of Fe²⁺ in the M1, M2, and M3 positions. The results of the MO calculations are in quantitative agreement with experiment and reveal that differences in the quadrupole splittings (ΔE _Q ), their temperature dependence and in the isomer shifts (δ) of Fe²⁺ in M1, M2, and M3 positions can theoretically by justified. Therefore, the combined Mössbauer and MO investigation shows that the three Fe²⁺ lattice sites in the chlorites investigated here can be discriminated according to their ΔE _Q -δ parameter pairs. With the calculated average iron-oxygen bond strength, the MO study provides an explanation for the observed trend that the population of the three lattice sites by Fe²⁺ increases according to the relation M1?相似文献