Temperature dependence of the cation distribution in nickel aluminate (NiAl2O4) spinel: a powder XRD study

NiAl₂O₄ is a largely inverse spinel, which in detail shows increasing randomisation with temperature of Ni and Al between the octahedral and tetrahedral cation sites of the spinel structure. We have used powder XRD to determine this cation distribution in various samples of NiAl₂O₄ quenched after annealing between 700 and 1400° C. The inversion parameter (x) can be measured with a precision of ± 0.004 (one standard deviation), and a comparison of different methods of synthesis, X-ray diffraction and refinement techniques, suggests a probable accuracy of better than 0.01. The results are supported by some preliminary single crystal refinements on flux-grown samples.Below 800° C the rate of cation ordering becomes very slow, and, despite reaching an apparently steady state, it is doubtful if our samples attained complete internal equilibrium. Above 1250° C the cation redistribution becomes so fast that the quenching method becomes unreliable. Between 800 and 1250° C inclusive, the degree of inversion changes smoothly from 0.87 at 800° C to 0.79 at 1250° C, and is accompanied by linear changes in u, the oxygen parameter, from 0.2555 to 0.2563 (±0.0002), and a₀, the lattice parameter, from 8.0462 to 8.0522 Å (±0.0002 Å).     

Sedimentological effects and palaeoecological implications of the tube-building polychaete Lanice conchilega Pallas

The tube-building polychaete Lanice conchilega forms intertidal mounds in association with macroalgae. This assemblage produces structures that can record tidal and seasonal cycles in the stratigraphic record. They mark low-tide levels because the assemblage occurs below neap low tide and many of the structures form when water drains off the assemblage. Mounds are created by disturbance of the sediment surface around aggregations of the assemblage and accumulation of sediments within the aggregations. The initial aggregations may be relict patches of adult worms, new clumps of juveniles or both. Juvenile worms and drift algae easily settle and survive in high-density patches, whereas predators and waves more readily disturb low-density patches. Algae and tubes extend through accumulated sediment and create a new, higher surface. Through this interactive process the high-density patches increase height rapidly while the low-density patches erode. Regardless of density, when the initial distribution is regular the surface remains flat, rising evenly or eroding evenly. Accumulation and erosion increases during spring tides and decreases during neap tides. Mound development also follows a seasonal pattern. The recruitment of juvenile worms in spring facilitates algal settlement and initiates mound buildup. The rate of tube-building and algal growth increases in early summer as the erosive forces of storms decline. This leads to the greatest development of mounds in late summer just before the macroalgae begin to die. The loss of algae coincides with autumnal storms, and causes catastrophic erosion of the mounds into relict patches of dormant tube-worms. Patches of tubes that survive the winter enhance spring recruitment and renewal of mound development. The shape of the mounds is often obscured during burial and preservation. Because of this, it may be difficult to distinguish the original form of ancient mounds without contemporaneous cementing organisms. But cycles of deposition and erosion are recorded in Lanice tubes and other biogenic structures. These structures can be used in conjunction with physical structures to define tidal height, seasonality or current regime. In general however, the presence of tube aggregations per se is not diagnostic of a specific hydraulic environment.     

Long-term dynamics of phosphorus in the Narochanskie Lakes and factors determining it

The Narochanskie Lakes (Batorino, Myastro, and Naroch) (Belarus) are a focus of many-year hydroecological studies. The modern evolution of the ecosystem of the lakes includes four stages: anthropogenic eutrophication in the 1970s, de-eutrophication because of nature protection measures in their drainage area in the 1980s, benthification because of invasion of mollusk-filterer Dreissena polymorpha Pallas in the 1990s, and the present-day state. Retrospective analysis of many-year dynamics of total phosphorus (1978–2010) in water of the Narochanskie Lakes is given for different stages of their ecosystems restructuring. The complex response of water bodies comprising a single ecosystem to external impacts is described and its causes are discussed.     

Destabilization, interaction, and eruption of filaments on the sun and associated phenomena

A brief overview of the observation results of filament interactions on the Sun both from the Earth and from space at the TRACE, SOHO, STEREO, Hinode, and Yohkoh stations in white light, Hα, extreme UV (EUV), X rays, and a radio range is presented. Various filament collision cases, where filaments merge (or do not merge) or change their forms as a result of reconnection, are considered. Filament interactions are associated with flares, filament eruptions, and coronal mass ejections. The theoretical aspects of the observed phenomena are also considered.     

Composition,Age, and Origin of Cretaceous Granitic Magmatism on the Eastern Chukchi Peninsula

New geochronological and isotopic geochemical data are given, which make it possible to recognize two types of granitic rocks on the eastern Chukchi Peninsula. Early Cretaceous Tkachen and Dolina granitic plutons with zircon ages (U–Pb SIMS) of 119–122 and 131–136 Ma are related to the first type. They cut through Devonian–Lower Carboniferous basement rocks and are overlain by the Aptian–Albian Etelkuyum Formation. Basal units of the latter contain fragments of granitic rocks. Late Cretaceous Provideniya and Rumilet granitic plutons, which contain zircons with ages of 94 and 85 Ma (U–Pb SIMS), respectively, belong to the second type. They cut through volcanic–sedimentary rocks of the Etelkuyum and Leurvaam formations pertaining to the Okhotsk–Chukotka Volcanic Belt. In petrographic and geochemical features, the Early Cretaceous granitic rocks of the Tkachen Pluton are commensurable with I-type granites, while Late Cretaceous granite of the Rumilet Pluton is comparable to A₂-type granite. The Sr–Nd isotopic data provide evidence that from the Early Cretaceous Tkachen and Dolina plutons to the Late Cretaceous Provideniya and Rumilet plutons, the degree of crustal assimilation of suprasubduction mantle-derived melts increases up to partial melting of heterogeneous continental crust enriched in rubidium. An unconformity and various degrees of secondary alteration of volcanic–sedimentary rocks have been established in the Okhotsk–Chukotka Volcanic Belt, and this was apparently caused by transition of the tectonic setting from suprasubduction to a transform margin with local extension.     

Detection of blends in the vicinity of Zeeman lines

High resolution spectrograms taken in polarized light have revealed the presence of significant blending within the profiles of some important Zeeman multiplets of a large umbra. Wavelength and equivalent width of each depictable blend have been derived from the corrected spectrograms and some preliminary identifications have been made.     

Remote estimation of surficial seafloor properties through the application Angular Range Analysis to multibeam sonar data

The variation of the backscatter strength with the angle of incidence is an intrinsic property of the seafloor, which can be used in methods for acoustic seafloor characterization. Although multibeam sonars acquire backscatter over a wide range of incidence angles, the angular information is normally neglected during standard backscatter processing and mosaicking. An approach called Angular Range Analysis has been developed to preserve the backscatter angular information, and use it for remote estimation of seafloor properties. Angular Range Analysis starts with the beam-by-beam time-series of acoustic backscatter provided by the multibeam sonar and then corrects the backscatter for seafloor slope, beam pattern, time varying and angle varying gains, and area of insonification. Subsequently a series of parameters are calculated from the stacking of consecutive time series over a spatial scale that approximates half of the swath width. Based on these calculated parameters and the inversion of an acoustic backscatter model, we estimate the acoustic impedance and the roughness of the insonified area on the seafloor. In the process of this inversion, the behavior of the model parameters is constrained by established inter-property relationships. The approach has been tested using a 300 kHz Simrad EM3000 multibeam sonar in Little Bay, NH. Impedance estimates are compared to in situ measurements of sound speed. The comparison shows a very good correlation, indicating the potential of this approach for robust seafloor characterization.     

Concentration and Diffusion of Nutrients in the Interpore–Bottom Water System of the Ob River Estuary

Oceanology - On cruise 76 in 2019, the R/V Akademik Mstislav Keldysh completed the Gulf of Ob–Kara Sea slope transect. Samples of bottom water and two sediment layers 1 cm thick were obtained...     

“Pure” supernovae and accelerated expansion of the Universe

A special class of type Ia supernovae that is not subject to ordinary and additional intragalactic gray absorption and chemical evolution has been identified. Analysis of the Hubble diagrams constructed for these supernovae confirms the accelerated expansion of the Universe irrespective of the chemical evolution and possible gray absorption in galaxies.     

Hawking radiation of Kerr-de Sitter black holes using Hamilton-Jacobi method

Hawking radiation of Kerr-de Sitter black hole is investigated using Hamilton-Jacobi method. When the well-behaved Painleve coordinate system and Eddington coordinate are used, we get the correct result of Bekenstein-Hawking entropy before and after radiation but a direct computation will lead to a wrong result via Hamilton-Jacobi method. Our results show that the tunneling probability is related to the change of Bekenstein-Hawking entropy and the derived emission spectrum deviates from the pure thermal but it is consistent with underlying unitary theory.