Combined inelastic neutron scattering and solid-state DFT study of dynamics of hydrogen atoms in trioctahedral 1M phlogopite

Inelastic neutron scattering (INS) was used to study the vibrational dynamics of the hydrogen atoms in natural trioctahedral phlogopite, K_0.93Na_0.03(Mg_2.47Fe_0.22Al_0.16Fe_0.04Tl_0.06)[Si_2.84Al_1.16]O₁₀OH_1.71F_0.28Cl_0.01, within the 50–1,000?cm^?1 energy range. The INS spectra collected using direct geometry spectrometer SEQUOIA (ORNL) were interpreted by means of the solid-state DFT calculations covering both normal mode analysis and molecular dynamics. To optimize the structure and to calculate the vibrational modes under harmonic approximation, both a hybrid PBE0 and the AM05 functional were used, while the molecular dynamics calculations (60?ps/1?fs) were performed only with the computationally less-demanding AM05 functional. The main contributions to the dominant band within ~750–550?cm^?1 are symmetric and antisymmetric Mg–O–H bending modes, overlapping with the skeletal stretching and bending modes causing weaker secondary movements of H atoms of inner hydroxyl groups. Signatures of the Mg–O–H bending modes appear down to ~400?cm^?1, where a region of octahedra deformation modes starts. These deformations cause just shallow movements of the hydrogen atoms and are mirrored by the modes with close vibrational energies. The region from ~330?cm^?1 down to the low-energy end of the spectrum portrays induced vibrations of the H atoms caused by deformation of individual polyhedra, translational vibrations of the parts of the 2:1 layer relative one to another, and librational and translational vibrations of the layer. The main difference between the INS spectrum of dioctahedral Al-muscovite and trioctahedral Mg-phlogopite is that the Mg–O–H modes are all assigned to in-plane vibrations of the respective hydrogen atoms.     

The Ms = 7.0 Uureg Nuur earthquake of 15.05.1970 (Mongolian Altai): the aftershock process and current seismicity in the epicentral area

The aftershock process induced by the Ms = 7.0 Uureg Nuur earthquake, one of the largest events in the Altai, has been studied comprehensively. As an additional experiment, a temporary local network of seismic stations was deployed in 2006 in the epicentral area of the earthquake to gain more insights into the current tectonic activity. The aftershocks of the Uureg Nuur event were restricted to small faults in the interior of fault blocks rather than those being localized along border faults. Seismic activity across the directions of large faults has apparently been generated by a fault (in the Tsagaan Shuvuut Range) reactivated during the Uureg Nuur earthquake. The aftershock process, at its final phase, involved an adjacent crust block.     

Comet C/2002 T7 (LINEAR): Polarimetric and photometric studies

We present the results of polarimetric and photometric observations of dynamically new comet C/2002 T7 (LINEAR) at phase angles from 6° to 26°. During the observations, the comet was at a distance of 2.7–1.3 AU from the Sun and 1.7–2.0 AU from the Earth. The aperture polarimetry was made with the 2.6-m Shain telescope and the 1.25-m AZT-11 telescope of the Crimean Astrophysical Observatory and with the 0.7-m telescope of the Astronomical Institute of the Kharkiv National University during the period from November 21, 2003, to February 21, 2004. The wideband UBVRI and WRC (λ7228/1142 Å) filters and the narrowband GC (λ5260/56 Å) filter were used. The photometric observations of the comet were carried out on February 21, 2004, with narrowband filters isolated the BC (λ4845/65 Å) and RC (λ6840/90 Å) continuum and the C₂ emission (λ5140/90 Å). The phase-angle dependence of linear polarization of the comet has been obtained, and its parameters, such as the minimal polarization P _min = ?1.63%, the phase angle of the minimal polarization α_min = 10.6°, the inversion angle α_inv = 22.7°, and the slope of the phase curve at the inversion angle h = 0.24% per degree, were found. From the photometric observations, the following quantities have been obtained: the column density of molecules C₂ in the line of sight logN (C₂) = ?9.15 mol/cm² and their production rate log Q (C₂) = 27.11 mol/s, the spectral gradient of reflectivity for the dust S′(BC, RC) ≈ 3%/1000 Å, and the dust production parameter Afρ equal to 371 and 273 cm for the blue and red continuum ranges, respectively. According to these results, the physical parameters of comet C/2002 T7 are close to the average characteristics of typical dusty comets.     

Traces of cometary material in the area of the Tunguska impact (1908)

A short overview of the studies of the authors and their colleagues performed over many years, which resulted in the discovery of traces of cometary matter in the peat at the epicenter of the Tunguska catastrophe in 1908, is given here. In the epicenter of the Tunguska cosmic body (TCB) explosion, the shifts in the isotopic composition of hydrogen and carbon relative to their values for the upper and lower layers of the same column were found in the catastrophic layers of peat grown up in 1908. These shifts cannot be attributed to any known terrestrial processes: the conservation of mineral and organic dust in peat, peat humification, the emission of hydrocarbon gases from the Earth, climate changes, and other physical and chemical processes. In the catastrophic layers of the control peat columns, the isotopic shifts are absent. The isotopic data agree well with the increased concentration of iridium and other platinum-group elements in the same peat layers, which is a reliable indicator of the presence of cosmic material in terrestrial objects. The cosmogenic character of the isotopic effects is confirmed by the presence of “dead” carbon (not containing radioactive ¹⁴C) in the catastrophic layers. To provide the shifts observed in the isotopic composition of carbon, cosmic carbon preserved in peat should be isotopically superheavy—from +50‰ to +60‰ according to calculations. Such isotopically heavy carbon is absent both on the Earth and in ordinary meteorites. It occurs only in individual mineral phases of CI carbonaceous chondrites, close to cometary dust in chemical composition, ratios of the content of iridium and other platinoids and rear-earth elements also points to the cometary nature of the TCB. In the near-catastrophic peat layers, the anomalous increase of the concentration of many volatiles was detected, which also suggests that the TCB was a cometary core. The studies of the content and the isotopic composition of nitrogen in the peat revealed traces of heavy acid rains induced by the flyby and explosion of the TCB.     

Mapping of underground cavities by the passive seismic standing waves method: the case study of Barsukovskaya cave (Novosibirsk region,Russia)

This article presents the results of mapping a karst cave by the passive seismic standing waves method. Barsukovskaya cave is located about 100 km southeast of the city of Novosibirsk (Russia). The total length of the cave's passages and grottoes is estimated at about 200 m, the maximum depth from the earth's surface is about 19 m. The method for studying underground cavities used is based on the effect of the generation of standing waves by microtremor in the space between the earth's surface and the cave roof. The accumulation of amplitude spectra of a large number of microtremor records makes it possible to determine the frequencies of the first few modes of these waves. Areal passive seismic survey on the earth's surface above the cave made it possible to construct a map of the lowest mode frequency distribution over the cave roof. Since no standing waves were observed at other points, this map reflects the cave structure in plan, which confirms the comparison with the cave diagram drawn up earlier by one of the speleologists. A schematic map of the depth of the cave roof was constructed using the longitudinal wave velocity V_p = 3120 m/s determined by the rock samples selected near the entrance to the cave. This map at a qualitative level also agrees with the data of speleologists, which indicate that the cave, on average, gradually becomes deeper from the entrance to its dead‐end branches. The shallower depths in comparison with the data of speleologists are apparently explained by a very low estimate of the velocity determined from a rock sample taken near the entrance to the cave. The reliability of the obtained cave mapping results is confirmed by the numerical simulation results using the finite‐element method.     

Groundwater chemistry in intrapermafrost taliks in Central Yakutia

An intrapermafrost aquifer system, which is widespread in the sand deposits of bestyakhskaya terrace of the Lena R. (Central Yakutia), is characterized by generalized data of many-year studies of its groundwater chemistry. The groundwater discharges onto land surface through high-yield springs. The largest such source forms the Ulakhan-Taryn Creek with a mean many-year yield of 20 740 m³/day. The results of generalization were used to show the chemistry of intrapermafrost water to be stable at both many-year and annual scales, to characterize the hydraulic interaction of intrapermafrost water with suprapermafrost and subpermafrost water, to assess the spatial variations of groundwater resources in the intrapermafrost aquifer from the head-formation to the discharge domain. The results of the study are of importance for solving the problem of centralized drinking water supply to large populated localities in the Central Yakutia, including Yakutsk City.     

Platinum group element abundances in a peat layer associated with the Tunguska event, further evidence for a cosmic origin

We have measured excesses of Pd, Rh, Ru, REE, Co, Sr, and Y in a peat column from the Northern peat bog of the 1908 Tunguska explosion site. Earlier, in this peat column the presence of an Ir anomaly at the event layers (30- depth) has been found (Planet Space Sci. 48 (1998) 179). In these layers, Pd, Rh, Ru, Co, Sr, and Y show pronounced anomalies of a factor 4-7 higher than the background value. In the event layers there are also good correlations between the siderophile platinum group elements (Pd, Rh, Ru) and Co, indicators of cosmic material, which imply they might have the same source, i.e. the Tunguska explosive body. The patterns of CI-chondrite-normalized REE in the event layers are much flatter than those in normal peat layers and different from those in the nearby traps. Furthermore, in these layers the patterns of CI-chondrite-normalized PGEs and the element ratios (e.g. C/Pd, C/Rh, and between some siderophile elements) give evidence that the Tunguska explosive body was more likely a comet, although we cannot exclude the possibility that the impactor could be a carbonaceous asteroid. We have estimated the total mass of a solid component of the explosive body up to 10³-10⁶ tons.     

电感耦合等离子体质谱分析通古斯大爆炸地区沉积物中超痕量铂族元素

建立了一个用酸（HF、HCI、HNO3、HCIO4）溶解通古斯地区沉积物样品，以Re为内标元素，用电感耦合等离子体质谱（ICP－MS）测定其中铂族元素的分析方法。方法检出限为0．001－0．06μg/L，回收率大于85％。用该方法分析了9个取自通古斯地区的沉积物样品，发现了Ru、Rh、Pd、Ir、Pt等元素的异常。