Plasma instability at the inner edge of the accretion disk—I

In this paper, the analytical and numerical results of the stability analysis of the accretion disk at the inner boundary is presented. Including the effect of finite conductivity in the disk dynamics, a simple calculation considering only the radial perturbation has been carried out. Within local approximation, it is concluded that the disk is stable to Kelvin-Helmholtz and resistive electromagnetic modes whereas the magnetosonic mode can destabilise the disk structure.     

The Influence of Storms on Water Quality and Phytoplankton Dynamics in the Tidal James River

Due to the unpredictable nature of intense storms and logistical constraints of sampling during storms, little is known about their immediate and long-term impacts on water quality in adjacent aquatic ecosystems. By combining targeted experiments with routine monitoring, we evaluated immediate impacts of two successive storm events on water quality and phytoplankton community response in the tidal James River and compared these findings to a non-storm year. The James River is a subestuary of the Chesapeake Bay and sampling was conducted before, during, and after Hurricane Irene and Tropical Storm (TS) Lee in 2011 and during the same time period (late summer/early fall) in 2012 when there were no storms. We collected and compiled data on nutrient and chlorophyll a concentrations, phytoplankton abundance, nitrogen uptake, primary productivity rates, and surface salinity, temperature, and turbidity in the meso- and polyhaline segments of the James River. Hurricane Irene introduced significant amounts of freshwater over the entire James River and Chesapeake Bay watersheds, while rainfall from TS Lee fell primarily on the tidal fresh region of the James River and headwaters of the Chesapeake Bay. Dinoflagellates dominated the algal community in the meso- and polyhaline segments prior to the storms in 2011, and a mixed diatom community emerged after the storms. In the mesohaline river segment, cyanobacteria abundance increased after TS Lee when salinities were depressed, likely due to washout from the oligohaline and tidal fresh regions of the river. In 2012, dinoflagellates dominated the community in both segments of the river during late summer but diatoms were also abundant and their biomass fluctuated throughout the summer and fall. Cyanobacteria were not present in either segment. Overall, we observed that the high-intensity rainfall from Hurricane Irene combined with high flushing in the headwaters as a result of TS Lee likely reduced primary productivity and altered community composition in the mesohaline segment but not the more estuarine-influenced polyhaline segment. Understanding the influence of high freshwater flow with a short residence time associated with storms is key to the planning and management of estuarine restoration as such disturbances are projected to increase as a result of climate change.     

Hyperfine interactions and spin transfer between Cr3+ and Al3+ in a synthetic single crystal of Mg2SiO4. A theoretical approach to the interpretation of EPR data

The occurrence of Cr-Al pairs in Mg₂SiO₄ has been detected by EPR spectroscopy. In the case where Cr³⁺ replaces Mg at the M2 position three different neighboring Si sites may be substituted by Al³⁺, which should yield different superhyperfine interactions. A new spectrum is presented which shows the presence of two of these possible pair configurations. An assignment of the spectral features to a specific Cr-Al pair with Cr at M2 from the experimental data alone was not possible, therefore, MSX _α cluster calculations have been performed from which the differences in the superhyperfine interaction for the various pair configurations could be obtained. Best agreement with the data of the Cr³⁺(M2)-Al pair exhibiting the most intense group of lines in the EPR spectrum was obtained for the situation where Al³⁺ is at the Si position with the shortest distance to M2. The second observed Cr³⁺(M2)-Al pair, which is significantly weaker in intensity, could not yet be assigned.     

Garnet re‐equilibration by coupled dissolution–reprecipitation: evidence from textural,major element and oxygen isotope zoning of ‘cloudy’ garnet

The analysis of texture, major element and oxygen isotope compositions of cloudy garnet crystals from a metapelite sampled on Ikaria Island (Greece) is used to assess the model of growth and re‐equilibration of these garnet crystals and to reconstruct the pressure–temperature–fluid history of the sample. Garnet crystals show complex textural and chemical zoning. Garnet cores (100–200 μm) are devoid of fluid inclusions. They are characterized by growth zoning demonstrated by a bell‐shaped profile of spessartine component (7–3 mol.%), an increase in grossular from 14 to 22 mol.% and δ¹⁸O values between 9.5 ± 0.3‰ and 10.4 ± 0.2‰. Garnet inner rims (90–130 μm) are fluid inclusion‐rich and show a decreasing grossular component from 22 to 5 mol.%. The trend of the spessartine component observed in the inner rim allows two domains to be distinguished. In contrast to domain I, where the spessartine content shows the same trend as in the core, the spessartine content of domain II increases outwards from 2 to 14 mol.%. The δ¹⁸O values decrease towards the margins of the crystals to a lowest value of 7.4 ± 0.2‰. The outer rims (<10 μm) are devoid of fluid inclusions and have the same chemical composition as the outermost part of domain II of the inner rim. Garnet crystals underwent a four‐stage history. Stage 1: garnet growth during the prograde path in a closed system for oxygen. Garnet cores are remnants of this growth stage. Stage 2: garnet re‐equilibration by coupled dissolution–reprecipitation at the temperature peak (630 < T < 650 °C). This causes the creation of porosity as the coupled dissolution–reprecipitation process allows chemical (Ca) and isotopic (O) exchange between garnet inner rims and the matrix. The formation of the outer rim is related to the closure of porosity. Stage 3: garnet mode decreases during the early retrograde path, but garnet is still a stable phase. The resulting garnet composition is characterized by an increasing Mn content in the inner rim’s domain II caused by intracrystalline diffusion. Stage 4: dissolution of garnet during the late retrograde path as garnet is not a stable phase anymore. This last stage forms corroded garnet. This study shows that coupled dissolution–reprecipitation is a possible re‐equilibration process for garnet in metamorphic rocks and that intra‐mineral porosity is an efficient pathway for chemical and isotopic exchange between garnet and the matrix, even for otherwise slow diffusing elements.     

Modeling of coupled tide–wave–surge process in the Yellow Sea

A coupled wave–tide–surge model has been developed in this study in order to investigate the effect of the interactions among tides, storm surges, and wind waves. The coupled model is based on the synchronous dynamic coupling of a third-generation wave model, WAM cycle 4, and the two-dimensional tide–surge model. The surface stress, which is generated by interactions between wind and wave, is calculated by using the WAM model directly based on an analytical approximation of the results using the quasi-linear theory of wave generation. The changes in bottom friction are created by the interactions between waves and currents and calculated by using simplified bottom boundary layer model. In consequence, the combined wave–current-induced bottom velocity and effective bottom drag coefficient were increased in the shallow waters during the strong storm conditions.     

Subsurface structure derived from detailed gravity and magnetic investigations along the Pala-Maneri traverse of the Main Central Thrust,NW Himalaya

A detailed, integrated gravity and magnetic study across the Main Central Thrust (MCT) along the Pala-Maneri traverse in Uttaranchal, NW Himalaya was carried out. The gravity data was acquired using a CG-3 gravity meter with an accuracy of 0.005 mGal, while magnetic data was acquired using a proton precession magnetometer with a station interval of 20 m. Data was collected along a 11.7 km, NE-SW traverse from Pala to Maneri along the proposed route of a hydroelectric headrace tunnel. The measured variation in the gravity field was approximately 70 mGal, with two prominent highs recorded at distances of 0.5 km, 7.5 km and lows at 3.0 km, 10.5 km from Maneri. The gravity highs can be attributed to presence of high-density rocks along the thrust planes. The sharp gravity low recorded at 10.5 km distance possibly indicates a sympathetic fault of the MCT that is highly saturated with fluids (water). The broad gravity low between 2.5 km and 4.0 km distance is likely to represent the gravity signature of the MCT itself. The measured variation in the magnetic field was approximately 285 nT. The associated gravity and magnetic signatures located several faults along the traverse including presence of the MCT at Kumaltigad.     

Analysis of accelerograms recorded in the source zone of the 1995 Neftegorsk earthquake and computation of synthetic accelerograms

The strongest Neftegorsk earthquake, which occurred in 1995 in the northern part of the Sakhalin Island, was studied by the Epicentral Seismological Expedition, Schmidt Institute of Physics of the Earth, Russian Academy of Sciences. The performed observations yielded the unique accelerograms of strong aftershocks, which were then applied as a basis for detailed analyses. The recorded accelerations were in satisfactory compliance with the current ground motion relations. The design spectra developed on the basis of analyzed records were proposed as an example. The synthetic accelerograms were calculated using the records of the strongest aftershocks for two modal earthquakes by the empirical Green’s function technique. This technique can be recommended for practical application as the most physically substantiated method taking into account all regional features.     

Optical identification of IRAS point sources based on low-dispersion spectra from the First Byurakan Survey. V

Part five of optically identified point sources from the IRAS Point Source Catalog (PSC) contains data on 19 late-type stars. The identifications were based on the Digitized Sky Survey (DSS), the First Byurakan Survey (FBS), blue and red maps of the Palomar survey (POSS), and infrared fluxes at 12, 25, 60, and 100 mm in the region of +61° ≤ δ ≤ +65° and 05 ^h 30 ^m ≤ α ≤ 18 ^h 35 ^m with an area of 357 sq. deg. Of the 76 objects given in the IRAS PSC as unidentified sources of infrared radiation, 51 are associated with known stars in existing catalogs, 6 are objects from the FBS of late-type stars, and 19 sources remained unknown in the optical range. For the identified stars we determined the optical coordinates, their departures from the IR coordinates, the Vstellar magnitudes, the color indices CI,and the preliminary spectral subtypes. The objects have optical magnitudes in the range of 8 ^m −16 ^m .Gas-dust shells are assumed to exist around four of the sources. Finder charts from the DSS are given for 19 of the objects. Translated from Astrofizika, Vol. 42, No. 1, pp. 53–59, January–March, 1999.