Multi-element characterisation of glass shards from stratigraphically correlated rhyolitic tephra units

Late Quaternary rhyolitic tephra units, erupted from the Taupo Volcanic Zone, North Island, New Zealand, were sampled from four stratigraphically correlated sections. Nineteen glass-shard separates from these tephra units were analysed by spark-source mass spectrometry. Data for the rare earth and other trace elements are presented. A statistical analysis of these data suggests an identification and correlation of the samples which is similar to the field-determined stratigraphy.Massive airfall tephra units that have been deposited during a single eruptive episode appeared to be more uniform in elemental concentrations than either multiple-bedded airfall tephra units, or tephra units comprising both airfall and airflow material which were considered to result from multiple-phase eruptions.The rare-earth element chondrite-normalised patterns showed enrichment of the lighter elements compared with the heavier elements. A notable Eu deficiency was recognised which was consistent with the model for enrichment of Eu in the plagioclase feldspars in acidic magma.     

Thermalization of solar wind

Three kinetic equations describing the linear and non-linear wave-particle interaction for an anisotropic solar wind plasma have been developed. These equations have been solved numerically to find the variation inT /T with respect to time, whereT andT are the perpendicular and parallel temperatures with respect to the ambient magnetic field of the solar wind. For wave energy greater than a critical value (strong turbulence), non-linear wave-particle interactions are important but do not lead to thermalization. On the other hand, weak nonlinear interactions tend to increaseT /T , but make only a negligible contribution in the quantitative sense. Thus, only the linear wave-particle interaction remains as the significant contributer to the increase ofT /T .     

Multidecadal changes in the relationship between extreme temperature events in Uruguay and the general atmospheric circulation

We analyze changes in the relationship between extreme temperature events and the large scale atmospheric circulation before and after the 1976 climate shift. To do so we first constructed a set of two temperature indices that describe the occurrence of warm nights (TN90) and cold nights (TN10) based on a long daily observed minimum temperature database that spans the period 1946?C2005, and then divided the period into two subperiods of 30?years each (1946?C1975 and 1976?C2005). We focus on summer (TN10) and winter (TN90) seasons. During austral summer before 1976 the interannual variability of cold nights was characterized by a negative phase of the Southern Annular Mode (SAM) with a cyclonic anomaly centered off Uruguay that favoured the entrance of cold air from the south. After 1976 cold nights are associated not with the SAM, but with an isolated vortex at upper levels over South Eastern South America. During austral winter before 1976, the El Ni?o phenomenon dominated the interannual variability of warm nights through an increase in the northerly warm flow into Uruguay. However, after 1976 the El Ni?o connection weakened and the variability of warm nights is dominated by a barotropic anticyclonic anomaly located in the South Atlantic and a low pressure center over South America. This configuration also strengthens the northward flow of warm air into Uruguay. Our results suggest that changes in El Ni?o evolution after 1976 may have played a role in altering the relationship between temperature extreme events in Uruguay and the atmospheric circulation.     

Absolute broad-band polarization behaviour of PSR B0329+54: a glimpse of the core emission process

In this paper we report multifrequency single-pulse polarization observations of the PSR B0329+54 normal mode using the Giant Metre-wave Radio Telescope at 325 and 610 MHz and the Effelsberg Observatory at 2695 MHz. Our observations show that towards the central part of the polarization position angle traverse there is an unusual 'arc'-like structure, which comprises a broad-band 'kink' and a frequency-dependent 'spot'. The features are intimately connected with the intensity dependence of the core component: the stronger emission arrives earlier and its linear polarization is displaced farther along the 'kink'. Moreover, at high intensities, the circular polarization is −/+ antisymmetric; the nearly complete positive circular is characteristic of the weaker, later core subpulses. We find that the 'kink' emission is associated with the extraordinary (X) propagation mode, and hence propagation effects do not appear to be capable of producing the core component's broad-band, intensity-dependent emission. Rather, the overall evidence points to a largely geometric interpretation in which the 'kink' provides a rare glimpse of the accelerating cascade or height-dependent amplifier responsible for the core radiation.     

NanoSIMS: Insights to biogenicity and syngeneity of Archaean carbonaceous structures

NanoSIMS is a relatively new technology that is being applied to ancient carbonaceous structures to gain insight into their biogenicity and syngeneity. NanoSIMS studies of well preserved organic microfossils from the Neoproterozoic (0.8 Ga) Bitter Springs Formation have established elemental distributions in undisputedly biogenic structures. Results demonstrate that sub-micron scale maps of metabolically important elements (carbon [C], nitrogen [measured as CN ion], and sulfur [S]) can be correlated with kerogenous structures identified by optical microscopy. Spatial distributions of C, CN, and S in individual microfossils are nearly identical, and variations in concentrations of these elements parallel one another. In elemental maps, C, CN, and S appear as globules, aligned to form remnant walls or sheaths of fossiliferous structures. The aligned character and parallel variation of C and CN are the strongest indicators of biogenicity.Nitrogen/carbon atomic ratios (N/C) of spheroids, filaments, and remnants of a microbial mat suggest that N/C may reflect original biochemical differences, within samples of the same age and degree of alteration. Silicon (Si) and oxygen (O) maps illustrate that silica is intimately interspersed with organic carbon of the microfossils. This relationship is likely to reflect the process of silica permineralization of biological remains and thus may be an indicator of syngeneity of the fossilized material with the mineral matrix.The NanoSIMS characterization of Bitter Springs microfossils can be used as a baseline for interpreting less well preserved carbonaceous structures that might occur in older or even extraterrestrial materials. An example of such an application is provided by comparison of Bitter Springs results with NanoSIMS of Archaean carbonaceous structures from Western Australia, including a spheroid in the 3 Ga Farrel Quartzite and material in a secondary vein in the 3.43 Ga Strelley Pool Chert. Results reinforce a biogenic, syngenetic interpretation for the Archaean spheroid.NanoSIMS has several advantages in the study of ancient organic materials: the technique allows characterization of extremely small structures that are present in low concentrations; organic matter does not have to be isolated by acid treatment but can be analyzed in polished thin section; preparation is simple; samples are minimally altered during analysis; results provide sub-micron scale spatial distribution coupled with concentration information for at least five elements; the biologically important elements of carbon and nitrogen can be assessed; and the ability to study organic remains in situ permits petrographic assessment of spatial relationships between organic matter and mineral constituents. These advantages could be of significant benefit for interpretation of poorly preserved and fragmentary carbonaceous remains that might occur in some of Earth's oldest samples as well as in meteorites or extraterrestrial material brought to Earth in future planetary missions.     

Microlite transfer by disaggregation of mafic inclusions following magma mixing at Soufrière Hills volcano,Montserrat

The Soufrière Hills volcano on Montserrat has for the past 12 years been erupting andesite with basaltic to basaltic–andesite inclusions. The andesite contains a wide variety of phenocryst textures and strongly zoned microlites. Analysis of minor elements in both phenocrysts and microlites allows us to put detailed constraints on their origins. Compositions of clinopyroxene, from overgrowth rims on quartz and orthopyroxene and coarse-grained breakdown rims on hornblende, are identical to those from the mafic inclusions, indicating that these rims form during interaction with mafic magma. In contrast, resorbed quartz and reversely zoned orthopyroxenes form during heating. Microlites of plagioclase and orthopyroxene are chemically distinct from the phenocrysts, being enriched in Fe and Mg, and Al and Ca respectively. However, microlites of plagioclase, orthopyroxene and clinopyroxene are indistinguishable from the compositions of these phases in the mafic inclusions. We infer that the inclusions disaggregated under conditions of high shear stress during ascent in the conduit, transferring mafic material into the andesite groundmass. The mafic component of the system is therefore greater than previously thought. The presence of mafic-derived microlites in the andesite groundmass also means that care must be taken when using this as a starting material for phase equilibrium experiments.     

Deep analyses of nulling in Arecibo pulsars reveal further periodic behaviour

Numerous studies of conal pulsars, e.g. B1133+16, have revealed fluctuation features and a steady null fraction. Sensitive Arecibo observations provide an unprecedented ability to detect nulls and confirm previously found fluctuation features. By replacing each pulse with a scaled version of the average profile, we were able to quench all subpulse modulation, dubbed pulse-modulation quelling (PMQ). It was surprising to note that the low-frequency feature observed in the natural longitude resolved fluctuation spectra (LRF) persisted in the PMQ LRFs. It appears that we can conclude, then, that in the natural pulse sequence the nulls themselves reflect whatever underlying periodicity is responsible for the low-frequency feature. Conversely, the aggregate fluctuation power of the low-frequency feature changes little whether the pulse modulation is quelled or not, implying that the feature fluctuations are produced by the nulls!     

Problème restreint des trois corps appliqué à un gyrostat

Résumé On étudie le mouvement d'un corpsS ₃ supposé non ponctuel, attiré par deux corps sphériques homogènes dont les masses sont prépondérantes vis à vis de la masse deS ₃. Le corpsS ₃ est muni de rotors et on recherche les cas d'équilibres apparents de ce corps lorsque son centre d'inertie occupe l'une des positions de LagrangeL ₁, ...,L ₅ du cas ponctuel. Des conditions suffisantes de stabilité de certaines solutions particulières sont obtenues.

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This paper is concerned with an extension of the classical restricted problem of three bodies when the smallest body is not considered to be a point mass. We assume that the smallest body consists of a solid hub and symetric rotors rotating at constant relative angular velocities. The mass center of the gyrostat satellite is presumed to occupy one of five librations pointsL ₁, ...,L ₅ of the classical restricted problem of three bodies. Assuming that the gyrostatic moment can have arbitrary constant values, we find the set of positions of relative equilibrium of the gyrostat satellite. We then proceed to define the domains of stability and instability.

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Un sujet proche du problème traité ici a été étudié par V. V. Rumyantsev (1974b).