Optical properties of dust from Jupiter family comets

To try to define specific physical properties of the dust of Jupiter-family comets (JFCs), we compare the light scattered by them. Amongst the more than 1000 JFCs, less than 200 are numbered, 40 of them being rather bright. In the present work we use data from the latter. In situ observations of three nuclei show low albedo surfaces. The albedo of the dust particles in the coma is low, with generally a red colour. The A(α)fρ product is a measure of cometary activity and secular changes. Images of different regions (jets and fans) give indications on the nucleus rotation and position of the emitting areas, as compared to the position of the rotation axis. Differences in physical properties between the particles in different regions are pointed out by differences in the linear polarization of the scattered light and by spectral variations in brightness and polarization. Jupiter family comets are considered as dust-poor comets. Tails and trails’ studies give an estimation of the size distribution of the particles. However the dust production rates depend on the largest particles (up to centimetre size), which are mainly observed in the trails where large dark compact particles are found. These dark particles are also responsible for the high polarization in the inner most coma of some comets. The meaning, in terms of physical properties, of the linear polarization is discussed through different examples such as 2P/Encke, 9P/Tempel 1 or the fragments of 73P/Schwassmann-Wachmann 3. Cometary outbursts and splitting events show that the properties of the dust ejected from the interior of the nucleus are similar to the ones of more active comets (new or with larger semi-major axis).     

Formalization of assessing radioactive waste burial site seismic regime parameters from seismological and geological data

A model is proposed that shows the relation of the block structure of the crust and earthquake sources (Sadovskii, 1979; Rodionov, 1979, 1984, 1994; Bugaev, 1999, 2011, 2014, 2015). The model can formalize how to assess the prediction of seismic regime parameters depending on the elastic limit and conditions and rate of deformation of the Earth’s crust. The spent nuclear fuel repository site in Olkiluoto (Finland) and a site in the area of the Krasnoyarsk Mining and Chemical Combine are considered as examples. It is demonstrated that the parameters of the prediction graphs limit the location of the points of magnitude repeatability graphs calculated for a site based on samples of earthquakes in the area according to different authors. This makes it possible to recommend predictive assessment of seismic regime parameters for stability monitoring of the seismic regime and safety analysis of a geological environment’s insulation properties for waste sites from the results of seismological monitoring and high-precision observations of modern movements of the Earth’s crust.     

Tectonics of southwestern Mexico,isotopic evidence,nuclear Central America,Late Cretaceous break up

In the paleogeographic reconstruction of Mexico and northern Central America, an ever-increasing amount of evidence shows that the entire region is a collage of suspect terranes transported from abroad, whose timing and sense of motion are now beginning to be understood. Among these, the Chortis block (nuclear Central America) and the Baja California Peninsula have been proposed as pieces of continent separated from the Pacific coast of southwestern Mexico, that have moved either southeastward by the Farallon plate or northwestward by the Kula plate. Previous studies mainly confined to the northern margin of the Chortis block, confirmed a left-lateral displacement of 130 km in Neogene time. Further studies made northwestward along the Mexican coast provided a better understanding of magmatic and metamorphic processes in the area, and suggested times of detachment increased to 30 Ma, 40 Ma, and 66 Ma. The pre-detachment westernmost position of the block has changed, depending on the model chosen, from Puerto Vallarta and beyond, to the current position. Here we show that the isotopic mineral ages from coastal granites along the coast from Puerto Vallarta, Jalisco (80 Ma) to Puerto Angel, Oaxaca (11 Ma) record systematic decrease of cooling ages from NW to SE. This pattern is interpreted to result from the progressive uplift of rocks exposed at the present-day coast in that direction, such uplift occurred in response to the development of the Middle America Trench at the newly formed continental margin when the Chortis block was sliding at an average rate of 1.5 cm/year in a sinistral sense to its present position. Our results also constrain the position of the Kula-Farallon spreading axis north of Puerto Vallarta. These observations led us to conclude that several indicators point to this time and region for the onset of strike-slip drifting of the Chortis block toward its current position. Here, we also present several view points in terms of other possilble interpretations to different tectonic, geologic and isotopic data sets published recently by different authors.     

Decay of a highly eccentric satellite

The re-entry phase of a highly eccentric satellite is discussed. Numerical simulations allowing the prediction of the exact date of re-entry of a highly eccentric satellite are exposed.It is shown that under very particular circumstances the life of the satellite can be extended by a few days. The number of final revolutions of the rapidly contracting orbit depends critically on the air density between 70 km and 100 km.Re-entry of the European scientific satellite HEOS-1 predicted for 28 October, 1975 is near such a situation.     

Über den Eisengehalt von Alumosilikaten aus Quarzknauern

Zusammenfassung Der Eisengehalt von Andalusiten und Disthenen aus Quarzknauern im Gebiet des Ötztaler—Stubaier Altkristallins wurde regional untersucht. Der Gehalt and Gesamteisen in primären Disthen liegt zwischen 0,17 und 0,22 Gew.% Fe₂O₃, während primäre Andalusite zwischen 0,26 und 1,93 Gew.% Fe₂O₃ schwanken. Dieser Unterschied in den Andalusiten wird auf ein wechselndes Angebot von Fe₂O₃ aus dem Nachbargestein der Knauern zurückgeführt.Ein Zusammenhang zwischen dem Eisengehalt der Andalusite und den verschiedenen Umwandlungsstadien Andalusit—Disthen konnte nicht nachgewiesen werden.

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On the iron content of alumosilicates in quartz nodules

Summary A determination of the regional distribution of the ironcontent of andalusites and kyanites in quartz-segregations of the Oetztal—Stubai crystalline complex gave values of 0.17–0.22% for the total iron in primary kyanite and 0.26–1.93% in andalusite. This difference is probably due to a variation in the Fe₂O₃-content in the country rocks of the quartz veins. No relationship between the iron-content in andalusite and the different stages of transformation from andalusite to kyanite could be established.

     

ON THE GENERATION OF P AND S WAVE ENERGY IN CRYSTALLINE ROCKS*

A seismic source consisting of a 700 kg weight that could be dropped vertically or projected down a ramp inclined at 45° to the vertical was tested as a source of P, SV and SH waves within a crystalline rock body at Chalk River, Ontario. The seismic energy was recorded by arrays of both horizontal and vertical-component geophones at distances between 30 and 600 m from the source, which was operated over glacial overburden varying in thickness from less than a meter to a few tens of meters. Seismic energy was more efficiently generated when the overburden thickness was at least several meters. The signals identified visually as S are generally true S, though some may be the converted wave PS. The SV amplitudes are generally larger than those of P, regardless of the type of shot, while the signal frequencies are roughly 60 Hz and 90 Hz, respectively. The horizontal-component seismograms for the inclined shots showed no evidence of SH polarization, and the SH amplitudes were only rarely enhanced relative to P and SV amplitudes on changing from vertical to inclined shots. These unexpected results are attributed to the combined effect of the high velocity and density contrasts and the irregularity of the boundary between the glacial overburden and the rock body.