Sodian stellerite from Capo Pula,Sardegna

The sodian stellerite (a zeolite) occurs as lustrous white or slightly pink, easily cleavable lamellae, filling cavities and fractures in an acid lava (andesite or rhyolite) in the cliff below S. Efisio Tower, near Capo Pula, Cagliari, Sardegna, Italy. The principal forms present are {010}, {011}, {111}. Single crystal photographs show an orthorhombic symmetry and Ammm (or Ammm) space group. An indexed X-ray diffraction powder pattern is provided. Unit cell dimensions, chemical formula, density, optical properties and thermal behaviour are given.     

Récherché du terme denième ordre des développements de l'astrodynamique

General expressions for the functionsE=f(M), r/a=f(M) anda/r=f(M) in the two-body problem are obtained as functions of eccentricitye without using Bessel functions.     

Les composantes du déplacement séculaire du pôle d'inertie de la Terre

After homogenizing the declination systems of the ILS Catalogue, the secular motion of the mean pole is studied. Our analyses leads to two components of this motion: a progressive component (already known) and an elliptical one.     

Vertumnite: Its crystal structure and relationship with natural and synthetic phases

Summary Vertumnite, Ca₄Al₄Si₄O₆(OH)₂₄·3H₂O, is metrically monoclinic, strongly pseudohexagonal;a=5.744 (5),b=5.766(5),c=25.12(1) Å, =119.72(5)°; space groupP2 ₁ /m. The crystal structure was determined from X-ray intensities and refined in both the monoclinic and the hexagonal space group [P6 ₃/m; a=(a _mon +b _mon )/2]. The monoclinic refinement did not lead to significant deviations from hexagonal symmetry. The atomic arrangement consists of modified brucite-layers Ca ₂ ^VII Al^VI(OH, H₂O)₈, atz=0 andz=1/2, alternating with tetrahedral double layers and connected only by hydrogen bridges. TheT sites are statistically and only partly occupied by Si and Al. The distances from theT sites to the three basal (O, OH) measure 1.80 Å; this large distance is probably caused by local deformations in connection with the disorder in theT sites. Water molecules occupy statistically the double rings. A comparison with the previously reported powder patterns of gehlenite hydrate and strätlingite is given.

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Vertumnit: Seine Kristallstruktur und seine Beziehungen zu anderen natürlichen und künstlichen Phasen

Zusammenfassung Vertumnit, Ca₄Al₄Si₄O₆(OH)₂₄·3 H₂O, ist metrisch monoklin, ausgeprägt pseudohexagonal;a ₀=5,744(5),b ₀=5,766(5),c ₀=25,12(1) Å, =119,72(5)°; RaumgruppeP2 ₁/m. Die Kristallstruktur wurde aus Röntgenintensitäten bestimmt und sowohl in der monoklinen wie in der hexagonalen Raumgruppe [P6 ₃/m; a ₀=(a _0,mon +b _0,mon )/2] verfeinert. Die monokline Verfeinerung führte auf keine wesentlichen Abweichungen von hexagonaler Symmetrie. Die Atomanordnung besteht aus modifizierten Brucit-Schichten, Ca ₂ ^VII Al^VI(Oh, H₂O)₈, die mit Doppeltetraederschichten abwechseln und mit diesen nur über Wasserstoffbrücken verbunden sind. DieT-Positionen sind durch Si und Al statistisch und nur partiell besetzt. Die Abstände von denT-Positionen zu den drei basalen (O, OH) messen 1,80 Å; dieser große Abstand wird wahrscheinlich durch lokale Verzerrungen im Zusammenhang mit der Unordnung in denT-Lagen verursacht. Wassermoleküle füllen statistisch die Doppelringe. Das Pulverdiagramm wird mit den publizierten Diagrammen von Gehlenit-Hydrat und Strätlingit verglichen.

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With 2 Figures     

Levynes and erionites from Sardinia,Italy

Three samples of levyne and two of erionite from three different localities of Sardinia are described. In two samples, levyne and erionite are intergrown by epitaxy. The levynes exhibit close chemical compositions with Ca>Na>K; as for their lattice constants, a is very similar in all three samples, while c of one sample is rather smaller than that of the other two. Unit cell dimensions of both erionites and chemical composition of one are also given. In addition, the following data are reported for the levynes: refractive indices for all three samples, density for two and DTA for one. The existence of levyne-erionite intergrowth is emphasized, and support is given to the idea that this intergrowth is much more common than the literature would suggest.     

Assessing statistical hurricane risks: nonlinear regression and time-window analysis of North Atlantic annual accumulated cyclonic energy rank profile

Natural Hazards - The ranking of events is a powerful tool to evaluate risks of catastrophic events. Here we analyze the rank-statistical profile of the North Atlantic annual accumulated cyclone...     

Linear and nonlinear oscillations of simple stellar models

A general property for the stability of the one zone model is derived in the case of linear nonadiabatic radial oscillations. The problem of the nonlinear adiabatic radial oscillations of the homogeneous model with a slow rotational velocity is discussed.     

The period distribution of eclipsing and spectroscopic binary systems,II

A statistical analysis of period distribution for eclipsing and spectroscopic binary systems, based on the spectral types of the components, shows several common features between the two independent samples. The similarity is increased if we eliminate the geometrical selection effect on the eclipsing binaries sample by means of the method described in previous papers. The period distribution becomes broader (and probably non-unimodal) for advanced spectral types.We also performed an analysis of the mean separation of systems as a function of the spectral type.     

A PRC relation for delta Scuti stars

The absolute radii of 78 Scuti variables in the Catalogue of the Geneva Observatory have been computed. A PRC relation among the period, radius and color has been obtained.     

Long-term radial velocity variations of o And

The results of radial velocity measures of the star o And from high dispersion plates relative to the years 1964, 1966, 1975 and 1976 are given. The averaged values of the 1964 and 1966 plates confirm the existence of the minimum in the trend of the radial velocities and fit well the curve obtained in the hypothesis of periodic long-term radial velocity variations with the period of 23.5 years (Fracassiniet al., 1977). Preliminary orbital elements in the hypothesis of a long period spectroscopic binary system have been tentatively drawn.