Mineralogical and geochemical features of graphitized rocks in the Chernorudka-Barakchin Tectonic Zone

The morphological and structural characteristics of graphite from the deep Chernorudka-Barakchin Fault Zone, Western Baikal region, are described. A complex of mineralogical investigations shows that graphite varieties of the Baikal region are characterized by a perfect structure. The most crystallographically regular samples are composed only of sp ²-carbon, whereas the virtually amorphous varieties are formed by sp ²-and sp ³-carbons as well. The characteristic features of the graphite varieties distinguish them from carbonaceous matter of metamorphic rocks. High concentrations of Co, Ni, Cr, Cu, Ti, Zn, Sc, V, S, Nb, Zr, Sr, Ba, Y, Nd, and La were detected while analyzing the microcomponent composition of the graphitized rocks. The majority of these elements are contained in microinclusions hosted in graphite. The elevated noble metal contents were established in graphitized metasomatic rocks, granitoids, and particularly, in graphite concentrates extracted from these rocks. Sulfides, native metals, and intermetallic compounds were detected in microinclusions. It is suggested that the inflow of reduced high-carbonaceous fluids was responsible for the transfer of chemical elements.     

Age and Melt Sources of Ultramafic Dykes and Rocks of the Bolshetagninskii Alkaline Carbonatite Massif (Urik-Iya Graben,SW Margin of the Siberian Craton)

Doklady Earth Sciences - The age of rocks of the Bolshetagninskii ijolite–syenite–carbonatite massif and ultramafic dykes within the Urik-Iya Graben in the southwestern part of the...     

Critical frequency foF2 as an indicator of trends in thermospheric dynamics

Variations with time during recent decades of three parameters are considered. R(foF2) is the correlation coefficient between the nighttime and daytime values of foF2 within the same day. Stable trends are found for minimal (R(foF2)(min)) and maximal (R(foF2)(max)) values of R(foF2) over the year. The foF2(day)/foF2(night) ratio demonstrates both negative and positive trends; the sign of the trend being governed by the inclination I and declination D of the magnetic field. The correlation coefficient r(h,fo) between foF2 and the 100-hPa level in the stratosphere demonstrates a decrease (both, for the years of maximum and minimum solar activity) from the 1980s to the 1990s. The trends in all three groups of data are considered in the scope of an assumption that there is a long-term change in the circulation in the upper atmosphere. The data considered in the paper provide an indirect confirmation of the existence of this change and show the possibility that further studies of the thermospheric dynamics can be undertaken using ground-based ionospheric observations.     

Long-Term Trends in the Critical Frequency of the E-layer

A search for trends k(foE) in the critical frequency of the ionospheric E layer at Juliusruh and Slough stations is performed by the method often used by the authors to analyze trends in the F2-layer parameters. It is found that k(foE) could differ in both magnitude and even sign within different time intervals. However, the k(foE) trends have been stably negative over the last two decades for both stations and all months of the year. The k(foE) values averaged over a year are ?0.012 and ?0.005 MHz per year for Juliusruh and Slough stations, respectively. The method used in the recent paper by La?tovi?ka et al. (2016) to determine foE trends is analyzed, and it is shown that the difference in linear approximation of the dependence of the observed foE values on F10.7 within different time intervals could be interpreted not as the presence of a different foE dependence on the F10.7 index within these intervals but as the presence within them of foE trends that change the slope of the linear approximation.     

Trends in Parameters of the F2 Layer and the 24th Solar-Activity Cycle

Geomagnetism and Aeronomy - Trends in foF2 are analyzed according to the data of Juliusruh and Boulder ionospheric stations to 2018. It is shown that the use of the traditional solar-activity...     

Comparison of several high-order advection schemes for vertex-based triangular discretization

Ocean Dynamics - Possible extensions of the standard 3rd (upwind) and 4th (centered) order vertex-centered finite-volume advection schemes on unstructured triangular meshes are explored. A...     

Parameters of oscillation generation regions in open star cluster models

We determine the masses and radii of central regions of open star cluster (OCL) models with small or zero entropy production and estimate the masses of oscillation generation regions in clustermodels based on the data of the phase-space coordinates of stars. The radii of such regions are close to the core radii of the OCL models. We develop a new method for estimating the total OCL masses based on the cluster core mass, the cluster and cluster core radii, and radial distribution of stars. This method yields estimates of dynamical masses of Pleiades, Praesepe, and M67, which agree well with the estimates of the total masses of the corresponding clusters based on proper motions and spectroscopic data for cluster stars.We construct the spectra and dispersion curves of the oscillations of the field of azimuthal velocities v _φ in OCL models. Weak, low-amplitude unstable oscillations of v _φ develop in cluster models near the cluster core boundary, and weak damped oscillations of v _φ often develop at frequencies close to the frequencies of more powerful oscillations, which may reduce the non-stationarity degree in OCL models. We determine the number and parameters of such oscillations near the cores boundaries of cluster models. Such oscillations points to the possible role that gradient instability near the core of cluster models plays in the decrease of the mass of the oscillation generation regions and production of entropy in the cores of OCL models with massive extended cores.     

Relation of the <Emphasis Type="Italic">F</Emphasis>2 region to stratospheric parameters: Dependence on magnetic activity in two solar cycles

The dependence of the correlation coefficient r(h, fo) between the stratospheric parameter h(100) and critical frequency foF2 revealed in the data of two solar cycles (1979–1989 and 1990–2000) on geomagnetic activity is analyzed. It is shown that the character of the r(h, fo) dependence on limitation on the Ap geomagnetic index is the same in both cycles but depends on the time of day and solar activity level for the given year. It is also found that there is a considerable difference in the absolute values of r(h, fo) between two cycles.     

Variations in <Emphasis Type="Italic">foF</Emphasis>2 at the end of the 1990s and beginning of the 2000s according to median data

Changes in the values of the critical frequency of the F2 layer from 1990 to 2005–2007, according to median data, are considered. Eleven stations, for which the necessary data are available, have been found in international databanks. The conclusion of the previous publication by Danilov (2011) that at the end of the 1990s and beginning of the 2000s a negative trend in foF2 was observed both after sunset and in the daytime is confirmed.