Changes in the Period of Negative Superhumps of Type SU UMa Dwarf Novae. II. NY Her (2017 and 2020)

Astrophysics - Photometric studies of the type SU UMa dwarf nova NY Her were made during 2017 and 2020 at the Crimean Astrophysical Observatory and at the Sanglokh Observatory over a total of 77...     

Detailed mineralogical-geochemical study of a large spinel Lherzolite xenolith in alkali basalt of Shavaryn Tsaram paleovolcano,Mongolia

Mineralogical-geochemical data obtained on a large xenolith of spinel lherzolite from basanites of Shavaryn Tsaram volcano (Middle Pleistocene) provide evidence that the xenolith was affected by heat and fluid that came from the basalt melt and induced geochemical heterogeneity of the xenolith. Olivine crystals from the central portion of the xenolith contain much more CaO than this mineral from the peripheral zones of the xenolith as well as in xenocrystals of the host basalts. The large xenolith was unevenly annealed by the host basalt melt, and this predetermined the heterogeneous diffusion-controlled “purification” of olivine crystals from their CaO admixture. The xenolith is heterogeneously enriched in LREE and some trace elements (Zr, Hf, Nb, Th, and U), and their distribution demonstrates unclearly pronounced concentric zoning: these elements enriched the outer portions of the xenolith. The enrichment of the xenolith in LREE and other mobile trace elements is explained by their occurrence not only as structurally bound (isomorphic) components in minerals but also in the form of nonstructural admixtures (contaminant), as minute grains of compounds hosted in the interstitial space and tiny cracks cutting mineral grains. The enrichment of the xenolith in these admixtures proceeded via their infiltration-controlled introduction with fluid from the basalt along minute cracks.     

Experimental investigation of atmospheric dispersion over the Swiss Plain — Experiment “SIESTA”

Between November 15 and 30, 1985, an international mesoscale transport experiment was performed on the Swiss Plain. Seven meteorological groups from Denmark, Germany, Italy and Switzerland measured diffusion properties of near neutral planetary boundary layers during six completely overcast days: four Bise (north-east wind) situations, one transitional situation and one west-wind situation. Diffusion was measured using SF₆ as tracer, which was released at the meteotower of the Gösgen nuclear power plant at 6 m above ground level. One hundred automatic samplers plus a mobile gas chromatograph were used to measure the concentration fields at distances up to 90 km downwind. Meteorological parameters were observed using radar-tracked constant-level balloons, tethered balloon soundings, sonic anemometers, an acoustic sounder and several meteorological ground stations, including a 110 m mast. All data were collected on a magnetic tape with free access to interested persons.The aim of the experiments was to obtain knowledge about the general nature of the turbulence, advection and atmospheric dispersion during neutral weak-wind situations over complex terrain. The collected data set will be useful for testing mesoscale transport and diffusion models. The results clearly show the channelling effect of the Jura mountains and the hilly prealpine region. An interesting result is that the SF₆ plumes showed intensive horizontal spread but only limited diffusion in the vertical direction.     

Die Schotteranalyse

Ohne Zusammenfassung     

The Eastern Congo—a beauty spot,rediscovered from a geological point of view

In East Africa, the feedback between tectonic uplift, erosional denudation and associated possible climate changes is being studied by a multidisciplinary research group, ‘Riftlink’. The group's focus is the Albertine Rift, the northern part of the western branch of the East African Rift System, and in particular the rising Rwenzori Mountains that stretch along the border of the D.R. Congo and Uganda. Major questions relate to the timing of the formation of the Rwenzori Mountains, and whether the height of these mountains (> 5000 m) relates to rift movements in Neogene times, or represents an old basement block that formed a topographic high long before. Though, at first, research concentrated on the eastern (Ugandan) part of the Albertine Rift and Rwenzori Mountains, it has now moved further to the west to the D.R. Congo. A first field‐campaign, covering the area from northern Lake Edward along the rift shoulder up to the Blue Mountains at Lake Albert, was conducted in summer 2009, in cooperation with the Ruwenzori State University of Butembo. Here, we present a brief overview of the field‐campaign, with impressions gathered on the morphology and geology of the study area.     

A meteorological 80-m tower near Rotterdam

Construction, observation site and instrumentation are described of an 80-m meteorological observation tower, erected in Vlaardingen, The Netherlands, for studies in connection with air pollution problems along the Nieuwe Waterweg. From measurements made regularly in the period April 1967–April 1968 summaries are given of wind profile parameters and gustiness averages. Case histories are presented of an air pollution episode lasting several days, and of an hourly average wind direction difference of 120 ° over 70 m.     

Variangular wind spirals

The term variangular is introduced to emphasize a significant difference between the present and certain earlier solutions to the problem of organized airmotion within the planetary boundary layer. The latter belong to the family of equiangular wind spirals and have the characteristic that the angle () formed by the vectors of shearing stress and geostrophic departure is invariant with height; it is shown that in this spiral-family, parabolic height-dependency of the effective (eddy) diffusivity (K) alone is permitted, including the asymptotic case of constant K; the famous Ekman spiral as well as the Rossby spiral are two prominent members of the family of equiangular wind spirals. The new variangular theory, as the name implies, permits variation of with height (z) and produces more versatile profiles of wind and stress due to less restraint in K (z). As an example of comparison with observed data, monthly mean wind profiles obtained at Plateau Station, Antarctica, are selected since they exhibit a noteworthy degree of variangularity, in relatively satisfactory agreement with properties of the new theoretical model for wind spirals.National Research Council Visiting Scientist Research Associate, Regional Environments Division, Earth Sciences Laboratory.     

Temperature,composition, and f O2 effects on intersite distribution of Mg and Fe2+ in olivines

Single-crystal X-ray structure refinement of natural olivines equilibrated at high temperature under controlled oxygen fugacity (f _O2) conditions, coupled with a structure-energy model were used to establish the influence of T, f _O2 and bulk chemistry on intracrystalline disorder.The results are: 1) The k _D (k _D = [(Fe M1·Mg M2)/(Fe M2·Mg M1)]) factor describing site population on M1, M2 polyhedra increases from values lower than 1 at T below 400–600° C (depending on composition) to values higher than 1 at higher temperature. 2) The increase of k _D with T is quite regular. 3) At constant temperature and pressure, k _D increases with increasing fayalite content in the mixture; 4) Contrary to previous observations (Will and Nover 1979; Nover and Will 1981) varying f _O2, within the stability range of the substance, has a negligible influence on intracrystalline disorder. 5) As ancillary results, the model confirms the defect scheme of Nakamura and Schmalzried (1983) for the investigated solids. Moreover, it shows that cationic vacancies are always created on M 1 site at the expense of Mg ions, while trivalent iron is always stabilized on M2 site. This explains the marked anisotropies observed in Fe-Mg interdiffusion (Buening and Busek 1973; Misener 1974; Schock et al. 1989).