Parameters of the spiral structure of the galaxy from data on δ Cephei stars

We determined the locations of Galactic spiral arm segments for various age groups from the available data on the positions, ages, radial velocities, and proper motions of 440 δ Cephei variables using a previously developed technique. We obtained such parameters of the Galactic spiral structure as the arm pitch angle, , and the pattern speed, Ω_P = 21.7 ± 2.8 km s^?1 kpc^?1, which are comparable to and Ω_P = 20.4 ± 2.5 km s^?1 kpc^?1, respectively, determined previously from open star clusters. Based on the radial velocities and proper motions of the sample stars, we derived the rotation curve of the Galaxy for the range of Galactocentric distances approximately from 6 to 15 kpc. Using the pattern speed, we determined the positions of the corotation region and the inner and outer Lindblad resonances. We estimated the perturbation amplitudes of the Galactic velocity field, f _R = ?1.8 ± 2.5 km s^?1 and f _? = +4.0 ± 3.4 km s^?1.     

Optimization fitting of the eccentric dipole models to the observed geomagnetic field

We have obtained formulas to calculate the field components of an eccentric dipole (ED) with an arbitrarily directed moment from specified coordinates of the dipole center and from its moment vector. With these formulas, the model dipole position was fitted to the observed geomagnetic field, and the approximation accuracy was estimated according to the standard deviation from IGRF along the X, Y, and Z components; the fitting procedure was checked in several tests.We computed the ED parameters (position and moment orientation) and harmonic coefficients of the ED field for 50 years using surface IGRF components, discovered some changes, and compared them with those according to the Schmidt eccentric dipole model. It was found that the nondipolar contributions to the geomagnetic field increase as the dipole field decays with time, and the dipole center drifts northand eastward away from the Earth's gravity center.The main contribution of the dipole part in the Gaussian spherical harmonic expansion of the geomagnetic field turned out to come from the terms with n of 1 to 5 rather than from two first terms, and the contribution of higher harmonics increases with time. Therefore, the Schmidt ED approximation based on the first eight Gauss coefficients (n ≤ 2) must have only relative significance indicating changes of the parameters. On the other hand, world magnetic anomalies (WMA) show up already in two first Gauss terms rather than since the third term as it has been commonly assumed.     

The crystal structure of loparite: a new acentric variety

Mineralogy and Petrology - The crystal structure of a new structural variety of loparite (Na0.56Ce0.21La0.14Ca0.06Sr0.03Nd0.02Pr0.01)Σ=1.03(Ti0.83Nb0.15)Σ=0.98O3 from the Khibiny alkaline...     

Parker’s dynamo near the excitation threshold

A method of constructing asymptotic solutions for nonlinear mean-field dynamo equations near the excitation threshold is developed and applied to equations describing the solar dynamo in a Parker model. The form of solution obtained corresponds to the eigensolution for a kinematic dynamo, for the intensity of the generation sources at which self-excitation of the magnetic field begins (the so-called marginally stable eigenfunction). The wave amplitude is calculated.     

Zoning and sectoriality of monazite-(Ce) from granite pegmatites of the central and South Urals

Zonal and sectorial monazite-(Ce) crystals from ceramic granite pegmatites of the Adui pluton are enriched in Ce and La, whereas monazite from the miarolitic gemstone pegmatites at the western contact of the pluton are enriched in Nd, Sm, Gd, and Y. This difference is caused by earlier crystallization of ceramic pegmatites and higher temperatures of their formation (650–600°C for ceramic pegmatites and 550–300°C for miarolitic pegmatites). Monazites from ceramic and miarolitic pegmatites of the Adui pluton differ in La and Nd contents, but their compositional trend in La-Nd coordinates is similar to the variation in monazite composition from the early to late granite pegmatites in the Ilmeny Mountains. It is suggested that decrease in temperature is a factor controlling REE contents in monazite. Heterovalent P ↔ Si and REE ↔ Th, Ca isomorphism in the consecutive zones of growth pyramids in monazite is both unidirectional and wave-like. Monazite from granite pegmatites of the Adui pluton and Ilmeny Mountains crystallized mainly under slightly alkaline conditions.     

Systematics of rare earth elements, Th, Hf, Sc, Co, Cr, and Ni in the vendian pelitic rocks of the Serebryanka and Sylvitsa groups from the western slope of the Central Urals: A tool for monitoring provenance composition

This paper presents the first data on the systematics of rare earth elements (REE), Th, Hf, Sc, Co, Cr, and Ni and the Nd model ages of fine-grained aluminosilicate clastic rocks of the Serebryanka and Sylvitsa groups of the Vendian from the Kvarkushsko-Kamennogorskii meganticlinorium (western slope of the Central Urals). It was found that the REE distribution patterns of shales and mudstones of the two groups are similar to those of the majority of post-Archean fine-grained terrigenous complexes. The presence of pelitic rocks with Gd_N/Yb_N > 2.0 in a number of Vendian levels suggests a contribution from an Archean component in the composition of the fine aluminosilicate clastic material. This is probably also indicated by the high degree of heavy REE depletion in some mudstone samples. The REE systematics allow us to suppose a heterogeneity of Vendian paleocatchments and variations in their composition with time. The eroded areas had the most mature composition in the beginning of Serebryanka. Starting from the second half of Serebryanka, mafic and/or ultramafic rocks started playing a significant role in the provenances. The rocks of the lower portion of the Serebryanka Group show T_Nd(DM) values of about 2.0 Ga, whereas the upper part of the section is dominated by rocks with T_Nd(DM) ? 1.77–1.73 Ga. This indicates that during the Taninskaya and Koiva time periods, fine aluminosilicate clastic material was supplied into the sedimentation region mainly from the west, from the eastern areas of the east European platform, where Archean and Early Proterozoic crystalline complexes dominated. A decrease in model ages was related to the addition of juvenile mantle material to the mature continental crust. Such processes can be illustrated by the mafic-ultramafic complexes (Dvoretskii, Shpalorezovskii, Vil’vinskii, etc.) located in the field of Vendian sedimentary sequences, which show T_Nd(DM) values from 824 to 707 Ma. It was concluded that the history of the formation of an Early Vendian rift in the western slope of the central Urals included only one rifting event (rather than three, as was previously supposed), which was supported by a variety of recent geological and isotope geochemical data.     

Meridional circulation and dynamo-wave propagation

The effects of meridional circulation on the solar dynamo wave are investigated in the Parker approximation using WKB techniques. The meridional circulation can substantially prolong the activity cycle; however, in the framework of the approximation considered, it cannot reverse the direction of propagation of the dynamo wave. If the circulation speed is too high, the solution is concentrated near the pole and can no longer be described in the Parker approximation.