Mössbauer spectroscopic and x-ray powder diffraction studies of synthetic micas on the join annite KFe3AlSi3O10(OH)2-phlogopite KMg3AlSi3O10(OH)2     

G. J. Redhammer  E. Dachs  G. Amthauer 《Physics and Chemistry of Minerals》1995,22(5):282-294

Micas of the composition K(Fe_3–x Mg _x )AlSi₃ O₁₀(OH)₂ (x=0.6, 1.2, 1.8, 2.4 and 3.0, corresponding to ann₈₀phl₂₀, ann₆₀phl₄₀, ann₄₀phl₆₀, ann₂₀phl₈₀ and ann₀phl₁₀₀) were synthesized hydrothermally under controlled oxygen fugacity conditions. Lattice parameters a ₀ and b ₀ show a distinct linear decrease with increasing Mg content. With increasing ferric iron content a deviation from this linear trend is observed especially within iron rich samples. The tetrahedral rotation angle increases smoothly from 0° in annite to 9.1° in phlogopite. Mössbauer spectra show Fe²⁺ and Fe³⁺ on the octahedral M1 and M2 sites and partially also Fe³⁺ on the tetrahedral site. There is a smooth increase of the quadrupole splitting on both the M1 and the M2 site going from annite to phlogopite, probably due to changes in the lattice contribution to the electric field gradient, assuming a positive correlation between quadrupole splitting and distortion. Fe³⁺ contents, as determined by Mössbauer spectroscopy, versus oxygen fugacity shows that, depending on the composition of the micas, minimum amounts of Fe³⁺ are present. For ann₈₀phl₂₀ this minimum amount of Fe³⁺ is about 8% decreasing to about 1–2% Fe³⁺ for ann₂₀phl₈₀.The molar volume of each solid solution member has been estimated from the determined relations of the molar volume versus % Fe³⁺ contents, extrapolated back to 0% Fe³⁺. Plotting these volumes as a function of X_phl shows that negative excess volume occur in the annitephlogopite join, with the maximum deviation from ideality around X _phl=0.3. Margules volume parameters have been constrained as: Wv, AnnPhl=0.018±0.016 J/(bar.mol) and Wv, PhlAnn=-0.391±0.025 J(bar.mol) (three site basis).  相似文献   

A climate change simulation starting from 1935     

U Cubasch  G C Hegerl  A Hellbach  H Höck  U Mikolajewicz  B D Santer  R Voss 《Climate Dynamics》1995,11(2):71-84

Due to restrictions in the available computing resources and a lack of suitable observational data, transient climate change experiments with global coupled ocean-atmosphere models have been started from an initial state at equilibrium with the present day forcing. The historical development of greenhouse gas forcing from the onset of industrialization until the present has therefore been neglected. Studies with simplified models have shown that this cold start error leads to a serious underestimation of the anthropogenic global warming. In the present study, a 150-year integration has been carried out with a global coupled ocean-atmosphere model starting from the greenhouse gas concentration observed in 1935, i.e., at an early time of industrialization. The model was forced with observed greenhouse gas concentrations up to 1985, and with the equivalent C0₂ concentrations stipulated in Scenario A (Business as Usual) of the Intergovernmental Panel on Climate Change from 1985 to 2085. The early starting date alleviates some of the cold start problems. The global mean near surface temperature change in 2085 is about 0.3 K (ca. 10%) higher in the early industrialization experiment than in an integration with the same model and identical Scenario A greenhouse gas forcing, but with a start date in 1985. Comparisons between the experiments with early and late start dates show considerable differences in the amplitude of the regional climate change patterns, particularly for sea level. The early industrialization experiment can be used to obtain a first estimate of the detection time for a greenhouse-gas-induced near-surface temperature signal. Detection time estimates are obtained using globally and zonally averaged data from the experiment and a long control run, as well as principal component time series describing the evolution of the dominant signal and noise modes. The latter approach yields the earliest detection time (in the decade 1990–2000) for the time-evolving near-surface temperature signal. For global-mean temperatures or for temperatures averaged between 45°N and 45°S, the signal detection times are in the decades 2015–2025 and 2005–2015, respectively. The reduction of the cold start error in the early industrialization experiment makes it possible to separate the near-surface temperature signal from the noise about one decade earlier than in the experiment starting in 1985. We stress that these detection times are only valid in the context of the coupled model's internally-generated natural variability, which possibly underestimates low frequency fluctuations and does not incorporate the variance associated with changes in external forcing factors, such as anthropogenic sulfate aerosols, solar variability or volcanic dust.  相似文献   

Possible creep-related tilt precursors obtained in the Central Apennines (Italy) and in the Southern Caucasus (Georgia)     

F. Bella  P. F. Biagi  M. Caputo  G. Della Monica  A. Ermini  P. V. Manjgaladze  V. Sgrigna  D. O. Zilpimiani 《Pure and Applied Geophysics》1995,144(2):277-300

Daily averaged tilt component data from two sites of the Central Apennines (Italy) and of the Southern Caucasus (Georgia), respectively, revealed intermediate-term tilts as possible precursors to earthquakes (M=3.0÷4.7) which occurred in the above-mentioned seismic areas within a distance of 50 km from the sites. A good temporal correlation as well as a fair spatial correspondence between these residual tilts (with amplitude and duration of some microradians and months, respectively) and main shocks were pointed out, by removing both secular trends and seasonal thermoelastic effects from the raw tilts. An attempt was made to justify the above-mentioned results, based on the assumption that the observed intermediate-term preseismic tilts are the manifestation of aseismic creep episodes of comparable duration in the fault materials of thrust faults close to the tilt sites. The mechanism refers to a strain field slowly propagating from the preparation focal area to the tilt site, through crustal blocks separated by weak transition zones. This propagation is thought to be the cause of the local aseismic fault slip recorded by the tiltmeters. Previously, both discrete structures and strain propagation effects were revealed in the Central Apennines and are thought also to exist in the Southern Caucasus. As in the past, the rheological properties of fault materials are revealed as viscoelastic ones. In fact, creep equations obtained by applying several viscoelastic models on our data, proved to fit quite well some of the observed tilt precursors, producing viscosity and rigidity values very similar to those reported in literature.Professor Petr Viktorovich Manjgaladze died during the writing of this paper  相似文献   

Seasonal variations of diffuse solar radiation at Ilorin (8°32′N,4°46′E), Nigeria     

Moses G. Iziomon  Theophilus O. Aro 《Astrophysics and Space Science》1995,228(1-2):1-18

Hourly diffuse solar irradiance (H_d) and the corresponding global irradiance (H) falling on a horizontal surface at Ilorin (8°32N,4°46E), Nigeria has been measured for a period of fifteen months commencing from February, 1993. As expected, each monthly mean diurnal variation of H_d exhibits a mid-day maximum, while that of the ratio H_d/H exhibits a minimum. The month to month variations of these parameters are consequent on the dominant atmospheric conditions observed in the months concerned. The monthly average daily total of diffuse radiation (H_dm) was found to be highest in February, 1994 with a value of (3347 ± 45) Wm^–2day^–1, mainly due to the effects of Harmattan haze and thin clouds, while it was found to be lowest in November, 1993 and January, 1994 with a value of about 2500 Wm^–2day^–1. Similarly, the ratio of the monthly average daily total of diffuse radiation to the monthly average daily total of global radiation (H_dm/H_m) had the lowest value of 0.49 in the relatively clear sky month of November, 1993 and the highest value of 0.74 in the mainly cloudy month of August, 1993. On an annual average, the diffuse component constituted about 60% of the global solar radiation arriving on the ground at Ilorin, Nigeria primarily due to clouds and Harmattan haze which are seasonal, in addition to the constant background of molecular scattering.  相似文献   

Search for low energyν e,μ,τ andv e,μ,τ in coincidence with BATSE gamma ray bursts     

M. Aglietta  P. Antonioli  G. Badino  G. Bologna  C. Castagnoli  A. Castellina  V. L. Dadykin  W. Fulgione  P. Galeotti  F. F. Khalchukov  E. V. Korolkova  P. V. Kortchaguin  V. B. Kortchaguin  V. A. Kudryavtsev  A. S. Malguin  L. Periale  V. G. Ryassny  O. G. Ryazhskaya  O. Saavedra  G. Trinchero  S. Vernetto  C. Vigorito  V. F. Yakushev  G. T. Zatsepin 《Astrophysics and Space Science》1995,231(1-2):355-358

A search for low energy neutrinos of all flavours in correlation with 553 ray bursts detected by BATSE aboard the Compton Observatory has been performed by the LSD (Liquid Scintillator Detector) neutrino telescope. No excess ofe,, orv _e,, candidate has been detected by LSD during the time interval in which BATSE detected the 90% of the photon flux for any of the GRBs analyzed. Upper limits on the neutrino fluxes are given in the paper.  相似文献   

Measurements in N2-CH4(C2H2) discharges of reaction rates and thermochemical constants for Titan atmosphere study     

Ricard A  Cernogora G  Fitaire M  Hochard L  Kouassi N  Speller C  Vacher JR 《Planetary and Space Science》1995,43(1-2):41-46

The kinetic reactions in N2-xCH4(C2H2) gas discharges with x less than 1% have been studied by emission spectroscopy in the afterglow of D.C. discharges and by mass spectroscopy from radiolysis ionization using alpha particles. The pressure range is from several Torr to 100 Torr. At the end of N2 D.C. discharges at room temperature, for a residence time of about 10(-2) s, the dominant active species are the N atoms with density of 10(14)-10(15) cm-3 for N2 density of about 10(17) cm-3 (3 Torr), the N2(X,V) vibrational molecules with for example [N2(X,V = 10)] approximately 10(14) cm-3 and the electronic metastable molecules N2(A 3 sigma u +) with a density of 10(12) cm-3. In such conditions, the following kinetic reactions have been studied: N2(A) + N2(A) --> N2(C,B,V') + N2(X), N2(A) + N2(X,V>5) --> N2(X) + N2(B,V') in pure N2 post-discharges and N2(A) + CH4 --> products, C + N + M2 --> CN(B,V') + M2, N2(X,V>4) + CN --> N2(X) + CN(B,A,V'), in N2-1% CH4 post-discharges. The clustering reactions of N2-(1-5%)CH4(C2H2) gas mixtures after radiolysis ionization have been studied for the H2CN+ nN2 ions and the equilibrium constants have been determined in the temperature range T = 140-300 K.  相似文献   

The effect of an optically thin region on stability of an accretion disk around a supermassive black hole     

B. F. Liu  G. Z. Xie  K. F. Ji 《Astrophysics and Space Science》1995,225(2):299-314

We analyse conditions of the innermost portion of an accretion disk and establish a set of equations for this region. A stable innermost region may exist, which can probably explain the observed UV and X-ray spectra, avoiding the unstable emission. We then discuss the detailed radial structure of a disk around a black hole for typical AGN parameters and obtain different kinds of- relationships for different regions of a disk. On the basis of this, we discuss the stability. A new type of cycle is present, which we call a double S shaped cycle. In this cycle, the extent of accretion rate variability is much larger than that in dwarf nova cycles. This probably solves the problem of violent variability of AGN. In the meantime, the very high accretion rate at the hottest state in limit cycles in the unstable region may provide continuous injection of matter to the jet and power the relativistic motion of the jet.  相似文献   

A topological approach to understand a multiple-loop solar flare     

L. G. Bagalá  C. H. Mandrini  M. G. Rovira  P. Démoulin  J. C. Hénoux 《Solar physics》1995,161(1):103-121

We analyze the UV and X-ray data obtained by the SMM satellite for the flare starting at 02:36 UT on November 12, 1980 in AR 2779. From a detailed revision of the Ov emission, we find that the observations are compatible with energy being released in a zone above the magnetic inversion line of the AR intermediate bipole. This energy is then transported mainly by conduction towards the two distant kernels located in the AR main bipole. One of these kernels is first identified in this paper. Accelerated particles contribute to the energy transport only during the impulsive phase.We model the observed longitudinal magnetic field by means of a discrete number of subphotospheric magnetic poles, and derive the magnetic field overall topology. As in previous studies of chromospheric flares, the Ov kernels are located along the intersection of the computed separatrices with the photosphere. Especially where the field-line linkage changes discontinuously, these kernels can be linked in pairs by lines that extend along separatrices. Our results agree with the hypothesis of magnetic energy released by magnetic reconnection occurring on separatrices.  相似文献   

Noise storms and the structure of microwave emission of solar active regions     

V. M. Bogod  V. Garimov  G. B. Gelfreikh  K. R. Lang  R. F. Willson  J. N. Kile 《Solar physics》1995,160(1):133-149

Solar radio and microwave sources were observed with the Very Large Array (VLA) and the RATAN-600, providing high spatial resolution at 91 cm (VLA) and detailed spectral and polarization data at microwave wavelengths (1.7 to 20 cm - RATAN). The radio observations have been compared with images from the Soft X-ray Telescope (SXT) aboard theYohkoh satellite and with full-disk phoptospheric magnetic field data from the Kislovodsk Station of the Pulkovo Observatory. The VLA observations at 91 cm show fluctuating nonthermal noise storm sources in the middle corona. The active regions that were responsible for the noise storms generally had weaker microwave emission, fainter thermal soft X-ray emission, as well as less intense coronal magnetic fields than those associated with other active regions on the solar disk. The noise storms did, however, originate in active regions whose magnetic fields and radiation properties were evolving on timescales of days or less. We interpret these noise storms in terms of accelerated particles trapped in radiation belts above or near active regions, forming a decimetric coronal halo. The particles trapped in the radiation belts may be the source of other forms of nonthermal radio emission, while also providing a reservoir from which energetic particles may drain down into lower-lying magnetic structures.Presented at the CESRA-Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994.  相似文献   

Solar flare activity and the structure of the coronal neutral line     

G. A. Stewart  S. Bravo 《Solar physics》1995,160(2):331-341

In this study we analyse the positions of major flares from 1978 and 1979, with respect to the magnetic structure of the solar corona, as described by a potential field model. We find that major flares exhibit no strong association with the neutral line at the chromospheric level. However, when we calculate the neutral line's position at higher and higher altitudes in the corona, we find that major flares show an increasing tendency to be found close to these high-altitude coronal neutral lines. The correlation between flares and higher-altitude coronal neutral lines reaches a maximum at an altitude of 0.35R , and thereafter decreases as the neutral line is moved out to the source surface at an altitude of 1.50R . This indicates that major flares are strongly associated with coronal structure at the 0.35R level ( 250 000 km) - an altitude surprisingly high in the corona. This reinforces the idea that flares are associated with large-scale coronal magnetic fields and also indicates that the region of coronal magnetic topology important to solar flare processes may be larger than previously thought.  相似文献