Galactic orbits of globular clusters in the region of the Galactic bulge

Galactic orbits have been constructed over long time intervals for ten globular clusters located near the Galactic center. A model with an axially symmetric gravitational potential for the Galaxy was initially applied, after which a non-axially symmetric potential corresponding to the central bar was added. Variations in the trajectories of all these globular clusters in the XY plane due to the influence of the bar were detected. These were greatest for the cluster Terzan 4 in the meridional (RZ) plane. The globular clusters Terzan 1, Terzan 2, Terzan 4, Terzan 9, NGC 6522, and NGC 6558 always remained within the Galactic bulge, no farther than 4 kpc from the Galactic center.     

Physical parameters and dynamical properties of the multiple system ι UMa (ADS 7114)

We analyze the physical parameters, orbital elements, and dynamic stability of the multiple system ?? UMa (HD 76644 = ADS 7114). We have used the positions from the WDS catalog and our own observations on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and the 1.5-m Russian-Turkish Telescope (Antalya, Turkey). We have obtained more precise orbital parameters of the subsystems, and spectral types, absolute magnitudes, and masses of the components. The primary has Sp = F0 V?CIV, M = 1.7 ± 0.1M _??, T _eff = 7260 ± 70 K, and log g = 4.30 ± 0.07. The companion in the close Aa subsystem is most likely a white dwarf with a mass of approximately 1.0 ± 0.3M _??. The spectral types and masses of the components in the BC subsystem are M3V, M4V and 0.35 ± 0.05M _??, 0.30 ± 0.05M _??, respectively. The total mass is 3.4 ± 0.4M _??. The Aa subsystem probably has an orbital period of 4470^d = 12.2^y and an eccentricity of approximately 0.6. The outer subsystem seems to have a period of approximately 2084 yrs and an eccentricity of approximately 0.9. We have carried out simulations using the stability criteria and shown that for all possible variations in the component parameters, the multiple system is unstable on a time scale of less than 10⁶ years with a probability exceeding 0.98. Possible reasons for this instability are discussed.     

General characteristics of the geochemical evolution of silicic melts during the development of massive sulfide magmatic ore systems: Evidence from the investigation of melt inclusions

The investigation of melt inclusions in the minerals of volcanic rocks from the massive sulfide deposits of Siberia and the Urals revealed some specific features in the development of their magmatic ore systems. It was shown that the petrochemical and rare earth element compositions of melt inclusions reflect the geodynamic conditions of their formation: island arc conditions for the massive sulfide deposits of Rudny Altai, eastern Tuva, and the Salair Range and a back arc basin environment for the Yaman-Kasy deposit. The silicic melts of inclusions from the volcanic rocks of massive sulfide deposits show some specific features with respect to the contents of volatile components. In all of the ore deposits studied, fluorine content was always low (0.03–0.08 wt %), whereas chlorine content (0.13–0.28 wt %) was higher than the average value for silicic melts (0.17 wt %). There is a strong differentiation of water content in melt inclusions, both between deposits and between various volcanics from a single deposit. Ore-bearing melts show the highest water contents of 3.34–4.07 wt %. High Cu contents in the silicic melts of the Yubileinoe and Kyzyl-Tashtyg deposits (up to 7118 and 3228 ppm, respectively) may indicate the affinity of some ore components to particular silicic magmas. This is supported by the elevated contents of Cu in the porphyry Cu deposits of Romania (Valea Morii), Mongolia (Bayan Ula), and Bolivia. On the other hand, the silicic melts of inclusions from the molybdenum-uranium deposit of the Strel’tsovka ore field show high contents of another group of ore components (U and F).     

Geochronology of eruptions and parental magma sources of Elbrus volcano,the Greater Caucasus: K-Ar and Sr-Nd-Pb isotope data

Complex geochronological and isotope-geochemical studies showed that the Late Quaternary Elbrus volcano (Greater Caucasus) experienced long (approximately 200 ka) discrete evolution, with protracted periods of igneous quiescence (approximately 50 ka) between large-scale eruptions. The volcanic activity of Elbrus is subdivided into three phases: MiddleNeopleistocene (225–170 ka), Late Neopleistocene (110–70 ka), and Late Neopleistocene-Holocene (less than 35 ka). Petrogeochemical and isotope (Sr-Nd-Pb) signatures of Elbrus lavas point to their mantle-crustal origin. It was shown that hybrid parental magmas of the volcano were formed due to mixing and/or contamination of deep-seated mantle melts by Paleozoic upper crustal material of the Greater Caucasus. Mantle reservoir that participated in the genesis of Elbrus lavas as well as most other Neogene-Quaternary magmatic rocks of Caucasus was represented by the lower mantle “Caucasus” source. Primary melts generated by this source in composition corresponded to K-Na subalkali basalts with the following isotopic characteristics: ⁸⁷Sr/⁸⁶Sr = 0.7041 ± 0.0001, ƒ_Nd = +4.1 ± 0.2, ¹⁴⁷Sm/¹⁴⁴Nd = 0.105–0.114, ²⁰⁶Pb/²⁰⁴Pb = 18.72, ²⁰⁷Pb/²⁰⁴Pb = 15.62, and ²⁰⁸Pb/²⁰⁴Pb = 38.78. The temporal evolution of isotope characteristics for lavas of Elbrus volcano is well described by a Sr-Nd mixing hyperbole between “Caucasus” source and estimated average composition of the Paleozoic upper crust of the Greater Caucasus. It was shown that, with time, the proportions of mantle material in the parental magmas of Elbrus gently increased: from ∼60% at the Middle-Neopleistocene phase of activity to ∼80% at the Late Neopleistocene-Holocene phase, which indicates an increase of the activity of deep-seated source at decreasing input of crustal melts or contamination with time. Unraveled evolution of the volcano with discrete eruption events, lacking signs of cessation of the Late Neopleistocene-Holocene phase, increasing contribution of deep-seated mantle source in the genesis of Elbrus lavas with time as deduced from isotope-geochemical data, as well as numerous geophysical and geological evidence indicate that Elbrus is a potentially active volcano and its eruptions may be resumed. Possible scenarios were proposed for evolution of the volcano, if its eruptive activity were to continue.     

Generation of the low-frequency branch of acoustic emission in affected rocks

As follows from data analysis of physical modeling, the reaction of acoustic background oscillations to an external impact is well-defined under triaxial loading of a dry sandstone core in the low-frequency range (1–100 Hz). This phenomenon is explained by the generation of a low-frequency constituent of acoustic emission. A high correlation of oscillation dynamics (Klimontovich S entropy) is observed at frequencies of tens of hertz and tens of kilohertz in the absence of such a correlation in the intermediate frequency range; a synchronous increase in the oscillation level is also observed at low and high frequencies.     

Sulphide Segregation in Ferropicrites from the Pechenga Complex, Kola Peninsula, Russia

The Palaeoproterozoic Ni–Cu sulphide deposits of the PechengaComplex, Kola Peninsula, occur in the lower parts of ferropicriticintrusions emplaced into the phyllitic and tuffaceous sedimentaryunit of the Pilgujärvi Zone. The intrusive rocks are comagmaticwith extrusive ferropicrites of the overlying volcanic formation.Massive lavas and chilled margins from layered flows and intrusionscontain <3–7 ng/g Pd and Pt and <0·02–2·0ng/g Ir, Os and Ru with low Pd/Ir ratios of 5–11. Theabundances of platinum group elements (PGE) correlate with eachother and with chalcophile elements such as Cu and Ni, and indicatea compatible behaviour during crystallization of the parentalmagma. Compared with the PGE-depleted central zones of differentiatedflows (spinifex and clinopyroxene cumulate zones) the olivinecumulate zones at the base contain elevated PGE abundances upto 10 ng/g Pd and Pt. A similar pattern is displayed in intrusivebodies, such as the Kammikivi sill and the Pilgujärvi intrusion.The olivine cumulates at the base of these bodies contain massiveand disseminated Ni–Cu-sulphides with up to 2 µg/gPd and Pt, but the PGE concentrations in the overlying clinopyroxenitesand gabbroic rocks are in many cases below the detection limits.The metal distribution observed in samples closely representingliquid compositions suggests that the parental magma becamesulphide saturated during the emplacement and depleted in chalcophileand siderophile metals as a result of fractional segregationof sulphide liquids. Relative sulphide liquid–silicatemelt partition coefficients decrease in the order of Ir >Rh > Os > Ru > Pt = Pd > Cu. R-factors (silicate-sulphidemass ratio) are high and of the order of 10⁴–10⁵, andthey indicate the segregation of only small amounts of sulphideliquid in the parental ferropicritic magma. In differentiatedflows and intrusions the sulphide liquids segregated and accumulatedat the base of these bodies, but because of a low silicate–sulphidemass ratio the sulphide liquids had a low PGE tenor and Pt/Irand Cu/Ir ratios similar to the parental silicate melts. Duringcooling the sulphide liquid crystallized 40–50% of monosulphidesolid solution (mss) and the residual sulphide liquid becameenriched in Cu, Pt and Pd and depleted in Ir, Os and Ru. TheCu-rich sulphide liquid locally assimilated components of thesurrounding S-rich sediments as suggested by the radiogenicOs isotopic composition of some sulphide ores (     

The Pangean ice age: studies with a coupled climate-ice sheet model

 Application of an ice sheet model developed for the Pleistocene to the extensive Carboniferous glaciation on Gondwana yields an ice sheet which has several features consistent with observations. While complete deglaciation is not achieved without CO₂ changes, the Milankovich-induced fluctuations in ice sheet volume are comparable to Pleistocene glacial/ interglacial signals. This result is shown to hold for a large fraction of physically reasonable parameter space. The model also exhibits multiple equilibria and sharp bifurcations, as infinitesimal changes in the solar constant or precipitation can lead to a qualitatively different climate. The success of the model in predicting ice location in an environment quite different from the Pleistocene provides additional support for the robustness of the basic model physics and suggests that the model can be applied with some confidence to other pre-Pleistocene glaciations. Received: 30 June 1998 / Accepted: 5 January 1999     

Tropospheric disturbance of 17–21 December 1974 and its effect on microwave propagation

A number of troposphere-monitoring experiments were pressed into service during a large tropospheric disturbance which lasted for several days in December 1974. The experiments operated intensively included a monostatic Sodar system, a satellite radio beacon receiver at very low elevation angles, Meteorological Radiosondes, a 250-kW weather radar, a microwave LOS link and a microbarograph. This multi-pronged campaign yielded very useful results and the correspondences between various observations were striking. The Sodar and microwave link observations were visibly affected only when N reached a value of about –70 units; however, the satellite beacon observations showed anomalous behaviour even for lower N values. Rather spectacular coincidences occurred on one night: the large fading (up to 10 db) in the LOS link; highly disturbed conditions displayed in the entire Sodar range; the largest tropospheric effect on the satellite beacon system; and the most active superrefraction of the radar echoes. It was also noticed that these effects are obvious only during nights, while they remain masked or dampened in the sun-lit hours.     

Reflections on the history of research on large wood in rivers

Dynamics and functions of large wood have become integral considerations in the science and management of river systems. Study of large wood in rivers took place as monitoring of fish response to wooden structures placed in rivers in the central United States in the early 20th century, but did not begin in earnest until the 1970s. Research has increased in intensity and thematic scope ever since. A wide range of factors has prompted these research efforts, including basic understanding of stream systems, protection and restoration of aquatic ecosystems, and environmental hazards in mountain environments. Research and management have adopted perspectives from ecology, geomorphology, and engineering, using observational, experimental, and modelling approaches. Important advances have been made where practical information needs converge with institutional and science leadership capacities to undertake multi-pronged research programmes. Case studies include ecosystem research to inform regulations for forest management; storage and transport of large wood as a component in global carbon dynamics; and the role of wood transport in environmental hazards in mountain regions, including areas affected by severe landscape disturbances, such as volcanic eruptions. As the field of research has advanced, influences of large wood on river structures and processes have been merged with understanding of streamflow and sediment regimes, so river form and function are now viewed as involving the tripartite system of water, sediment, and wood. A growing community of researchers and river managers is extending understanding of large wood in rivers to climatic, forest, landform, and social contexts not previously investigated. © 2020 John Wiley & Sons, Ltd.