Chandra measurements of the X-ray core and cluster of 3C 220.1

We report results of an 18-ks exposure with the ACIS instrument on Chandra of the powerful z =0.62 radio galaxy 3C 220.1. The X-ray emission separates into cluster gas of emission-weighted kT ∼5 keV , 0.7–12 keV luminosity (to a radius of 45 arcsec) of 5.6×10⁴⁴ erg s⁻¹ and unresolved emission (coincident with the radio core). While the extended X-ray emission is clearly thermal in nature, a straightforward cooling-flow model, even in conjunction with a point-source component, is a poor fit to the radial profile of the X-ray emission. This is despite the fact that the measured properties of the gas suggest a massive cooling flow of ∼130 M_⊙ yr⁻¹, and the data show weak evidence for a temperature gradient. The central unresolved X-ray emission has a power-law spectral energy index α ∼0.7 and 0.7–12 keV luminosity of 10⁴⁵ erg s⁻¹, and any intrinsic absorption is relatively small. The two-point spectrum of the core emission between radio and X-ray energies has α _rx=0.75 . Since this is a flatter spectrum than seen in other sources where the X-ray emission is presumed to be radio-related, regions close to the active galactic nucleus (AGN) in this source may dominate the central X-ray output, as is believed to be the case for lobe-dominated quasars. Simple unification models would be challenged if this were found to be the case for a large fraction of high-power radio galaxies.     

Numerical Analysis of Space–Time Finite Element Formulations for Miscible Displacements

A finite element formulation is proposed to approximate a nonlinear system of partial differential equations, composed by an elliptic subsystem for the pressure–velocity and a transport equation (convection–diffusion) for the concentration, which models the incompressible miscible displacement of one fluid by another in a rigid porous media. The pressure is approximated by the classical Galerkin method and the velocity is calculated by a post-processing technique. Then, the concentration is obtained by a Galerkin/least-squares space–time (GLS/ST) finite element method. A numerical analysis is developed for the concentration approximation. Then, stability, convergence and numerical results are presented confirming the a priori error estimates.     

Seismic reflection survey of an oblique aseismic basement trend on the Reykjanes Ridge

A detailed (5 km track separation) seismic reflection survey of a portion of the upper flank of Reykjanes Ridge supports the existence of an oblique aseismic ridge, previously postulated from other data. The oblique basement ridge may have been formed by a magma center moving southwest under this portion of the Reykjanes Ridge at about 6 cm/yr between 7 and 5 mbyp. The oblique ridge is complex, being interrupted by saddles about every 30 km length. This spacing could reflect incipient, very weakly developed transverse fractures, or more probably the concentration of volcanic activity at particularly active vents, which shift southwestward every million years or so in response to the south-westward moving magma chambers entrained in the asthenosphere. Minor irregularities in the oblique ridge parallel crustal isochrons; such small features are probably elongate fissure eruptions restricted to a narrow spreading axis.     

Energy spectra and relative abundances of ions of C,O, and Fe at 1 AU during the quiet sun

The ion composition of fluxes of charged particles in interplanetary space with energies ∼0.03–10 MeV/nucleon are studied during quiet periods in the 23rd solar-activity cycle using data from the ACE spacecraft. Apart from the activity minimum, the Fe/O ratio during such periods corresponds to either the relative abundances of ions in particle fluxes accelerated in solar flares or the mean abundances of elements in the solar corona. At the cycle minimum, this ratio takes on values characteristic for the solar wind. These results indicate that the background fluxes of low-energy particles in the phases of the growth, maximum, and decay of the solar cycle include significant contributions from both coronal particles accelerated to suprathermal energies and particles accelerated in small impulsive solar flares. The particle fluxes from such flares are distinguished by an enhanced abundance of iron ions.     

Octahedral cation ordering in olivine at high temperature. I: in situ neutron single-crystal diffraction studies on natural mantle olivines (Fa12 and Fa10)

Crystallographic determinations on natural olivine single crystals of mantle composition and origin, carried out by in situ neutron diffraction at high temperature, show that the octahedrally co-ordinated Fe²⁺ and Mg cations undergo two successive trends of cation ordering with increasing temperature. An initial slight preference of Fe²⁺ for site M1, up to a temperature of about 850?°C, is followed by a reverse-ordering reaction with a site preference exchange between the two cations. The cross-over between the two regimes of ordering, corresponding to a situation of complete disorder, occurs at about 900?°C. Above this temperature Fe²⁺ progressively and strongly segregates into site M2 up to 1300?°C, the practical limit of the experimental setup utilized in the experiments. Care was taken to ensure that no chemical changes occurred in the crystals (i.e. oxidation), as testified by Mössbauer spectroscopy determinations carried out before and after the heat treatment. The cation-ordering behaviour is reflected in temperature-dependent changes of geometrical and atomic displacement parameters occurring in the octahedral sites M1 and M2. A thermodynamical explanation of this behaviour is proposed in terms of a prevailing vibrational contribution to entropy.     

Simulated precipitation response to SST forcing and potential predictability in the region of the South Atlantic convergence zone

The sensitivity of the precipitation response in the South Atlantic convergence zone (SACZ) to sea surface temperature (SST) anomaly is investigated by an inter-model comparison study of ensembles of multidecadal integrations of two atmospheric general circulation models (AGCMs)—version 1 of the NASA Seasonal-to-Interannual Prediction Project (NSIPP-1) model, and the NCAR community climate model (CCM3) version 3.6.6. Despite the different physical parameterizations, the two models consistently show an SST-forced signal located mainly over the oceanic portion of the SACZ. The signal has interannual-to-decadal timescales, and consists of a shift and strengthening of the SACZ toward anomalous warm waters. A potential predictability analysis reveals that the maximum predictable variance is about 50% of the total SACZ variance over the ocean, but the signal attenuates rapidly toward the South American continent. This result implies that the land portion of the SACZ is primarily dominated by the internal variability, thereby having a limited potential predictability at seasonal timescales.     

Determination of the concentration of chemical main and trace elements (chemical matrix) in the aerosol from 1972 to 1982 at a North-alpine pure air station at 1780 m a.s.l.

Summary Aerosol particles have been separated by filter at a mountain station at 1780 m a.s.l. continuously since 1972. The station (a WMO-BAPMoN station with extended program) is freely exposed to all sides and in no way influenced by local aerosol sources. In the cold seasons it lies almost exclusively above the convection layer (very often over inversions) so that real background data can be acquired in these cases. By means of analytical methods the chemical components are determined on the exposed filters. This includes (apart from crust elements) also cations and anions from man-made and maritime sources as well as some important trace elements (in all, 15 components). Filters are exposed over 1–4 days. Filter exchange is determined by the respective weather situation with due regard to all changes so that the requirements for a reasonable correlation of the measured values with the meteorological conditions are met. Additionally, all meteorological parameters are determined, as well as intensity of the vertical exchange, number density of Aitken nuclei, concentration of natural radioactivity (RaB), and other variables. In the present paper the components of the aerosol chemical matrix are related to the behavior of the parameters below and the results are discussed in detail: Dependence of the individual components on total aerosol mass per volume, type of air mass; representation of two single cases of long-range transport of crust elements (source areas: Sahara, Colorado); vertical exchange coefficient, concentration of natural radioactivity, temperature gradient between valley and mountain station, temperature at the sampling site, relative humidity, precipitation rate, wind direction. occurrence of fog.Zusammenfassung An einer allseitig frei exponierten Bergstation in 1780 m NN werden seit 1982 die Aerosolpartikel auf Filtern gesammelt. Die Station (eine WMO-BAPMoN-Station mit erweitertem Programm) wird nicht durch lokale Aerosolquellen in irgendeiner Weise beeinflußt. Sie liegt in den kalten Jahreszeiten fast ausschließlich über der Konvektionsschicht (sehr oft oberhalb von Inversionen), so daß in diesen Fällen echte Background-Daten erfaßt werden. Mittels analytischer Verfahren werden an den exponierten Filtern alle chemischen Hauptkomponenten (von den Krustenelementen abgesehen auch die Kationen und Anionen sowohl anthropogenen als auch maritimen Ursprungs), sowie einige gewichtige Spurenelemente (insgesamt 15 Komponenten) bestimmt. Die Filter werden 1–4 Tage lang exponiert. Der Filterwechsel wird durch den jeweiligen Wetterzustand bzw. seiner Veränderung gesteuert, so daß eine gute Voraussetzung für eine Zuordnung der Meßwerte zu den meteorologischen Bedingungen gegeben ist. Zusätzlich werden alle meteorologischen Parameter, sowie die Intensität des Vertikalaustausches, Zahl der Aitken-Kerne, Konzentration der natürlichen Radioaktivität (RaB) und andere Größen bestimmt. In der vorliegenden Arbeit werden die Komponenten der chemischen Aerosolmatrix zum Verhalten der folgenden Parameter in Beziehung gesetzt und die Ergebnisse eingehend diskutiert:Abhängigkeit der Einzelkomponenten von: Gesamt-Aerosohnasse pro Volumen; Typ der Luftmasse und Darstellung von zwei Einzelfällen eines Ferntransportes von Krustenelementen (Quellgebiete: Sahara, Colorado); vertikaler Austauschkoeffizient; Konzentration der natürlichen Radioaktivität; Temperaturgradient zwischen Tal- und Bergstation; Temperatur an der Probennahmestelle; relative Feuchte; Niederschlagsintensität; Windrichtung; Auftreten von Nebel.

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Bestimmung der Konzentration chemischer Haupt- und Spurenstoffe (chemische Matrix) im Aerosol von 1972 bis 1982 an einer nordalpinen Reinluftstation in 1780 m NN.Teil II: Parametrische Korrelationsanalyse der chemischen Matrix mit Berücksichtigung meteorologischer Größen

     

A canonical theory for short GPS baselines. Part IV: precision versus reliability

This contribution is the last of four parts and deals with the link between baseline precision and ambiguity reliability. It is shown analytically how and to what extent the baseline-ambiguity correlation is related to the gain in baseline precision, to the volume of the ambiguity search space, and to the impact of potential integer ambiguity biases. Also, an ambiguity DOP measure is introduced together with its closed-form formulae for the three different single-baseline models. Received: 16 July 1996 / Accepted: 14 November 1996     

Solar models with strong turbulence

A series of evolutionary models for the Sun were constructed using the strong turbulence model of the variable mixing-length theory (AMLT) of Canuto (1990). The present values of the solar model were obtained by an initial compositionX = 0.754,Z = 0.019, and(x) = 1.1. The physical variables which were obtained by applying the strong turbulence case of AMLT were similar to those of weak turbulence model (Kzlolu and Civelek, 1992) if we focused on the fitting of present solar radius and luminosity.