639 research outputs found
Pressure-induced spin-state transition of iron in magnesiow\"ustite (Fe,Mg)O
We present a detailed theoretical study of the electronic, magnetic, and
structural properties of magnesiow\"ustite FeMgO with in the
range between 00.875 using a fully charge self-consistent implementation of
the density functional theory plus dynamical mean-field theory (DFT+DMFT)
method. In particular, we compute the electronic structure and phase stability
of the rock-salt B1-structured (Fe,Mg)O at high pressures relevant for the
Earth's lower mantle. We obtain that upon compression paramagnetic (Fe,Mg)O
exhibits a spin-state transition of Fe ions from a high-spin to low-spin
(HS-LS) state which is accompanied by a collapse of local magnetic moments. The
HS-LS transition results in a substantial drop of the lattice volume by about
48 %, implying a complex interplay between electronic and lattice degrees of
freedom. Our results reveal a strong sensitivity of the calculated transition
pressure upon addition of Mg. While for Fe-rich
magnesiow\"ustite, Mg , exhibits a rather weak variation
at 80 GPa, for Fe-poor (Fe,Mg)O it drops, e.g., by about 35 % to 52 GPa
for Mg . This behavior is accompanied by a substantial change of the
spin transition range from 50140 GPa in FeO to 3090 GPa for . In
addition, the calculated bulk modulus (in the HS state) is found to increase by
12 % from 142 GPa in FeO to 159 GPa in (Fe,Mg)O with Mg . We
find that the pressure-induced HS-LS transition has different consequences for
the electronic properties of the Fe-rich and poor (Fe,Mg)O. For the Fe-rich
(Fe,Mg)O, the transition is found to be accompanied by a Mott insulator to
(semi-) metal phase transition. In contrast to that, for , (Fe,Mg)O
remains insulating up to the highest studied pressures, implying a Mott
insulator to band insulator phase transition at the HS-LS transformation.Comment: 9 pages, 9 figure
Theoretical and methodological grounds for the modernization of the tax administration system
The article stands for the theoretical underpinning of economic grounds of tax system and its building on the basis of social- and business-oriented socioeconomic features.
Authors proved the need for tax process management that represent the features of government-society-taxpayer relations with taxpayer’s leading role as macroeconomic tool for economic regulation process as well as providing the sustainable and balanced economic growth and innovative modernization of Russian economy.peer-reviewe
Classification of double flag varieties of complexity 0 and 1
A classification of double flag varieties of complexity 0 and 1 is obtained.
An application of this problem to decomposing tensor products of irreducible
representations of semisimple Lie groups is considered
Structured financial products as the instrument of financial credit assurance for the companies involved into foreign economic activities
© 2015, Mediterranean Center of Social and Educational Research. All rights reserved. Indefiniteness in financial markets motivates many market participants to use with increasing frequency the structured financial products. In the research paper at the level of concept we propose the structured financial products aimed at solution of pressing tasks faced by the companies involved into foreign economic activities
Domain evolution of BaTiO3 ultrathin films under electric field: a first-principles study
A first-principles-derived method is used to study the morphology and
electric-field-induced evolution of stripe nanodomains in (001) BaTiO3 (BTO)
ultrathin films, and to compare them with those in (001) Pb(Zr,Ti)O3 (PZT)
ultrathin films. The BaTiO3 systems exhibit 180o periodic stripe domains at
null electric field, as in PZT ultrathin films. However, the stripes alternate
along [1-10] in BTO systems versus [010] in PZT systems, and no in-plane
surface dipoles occur in BTO ultrathin films (unlike in PZT materials).
Moreover, the evolution of the 180o stripe domains in the BaTiO3 systems, when
applying and increasing an electric field along [001], involves four regions:
Region I for which the magnitude of the down dipoles (i.e., those that are
antiparallel to the electric field) is reduced, while the domain walls do not
move; Region II in which some local down dipoles adjacent to domain walls
switch their direction, resulting in zigzagged domain walls - with the overall
stripe periodicity being unchanged; Region III in which nanobubbles are
created, then contract along [110] and finally collapse; and Region IV which is
associated with a single monodomain. Such evolution differs from that of PZT
ultrathin films for which neither Region I nor zigzagged domain walls exist,
and for which the bubbles contract along [100]. Discussion about such
differences is provided.Comment: 19 pages, 4 figures, 27 references, submitted to Phys. Rev.
Critical phenomena in 1D Ising model with arbitrary spin
The aim of this work was to study critical phenomena taking place in 1D Ising model with different exchange interactions signs and arbitrary spin values in a magnetic field. Exact analytical formulas for frustration fields, zero temperature magnetization and entropy at these fields are obtained. The general behavior of pair spin correlation function with the accounting of only interactions between nearest neighbors is examined. © 2018 The Authors, published by EDP Sciences.The reflorted study was carried out within the state assignment of FASO of Russia (theme «Quantum» n. 01201463332) and was funded by RFBR according to the research flroject n. 16-32-00032
Arc Magmas from Slab to Eruption: The Case of Kliuchevskoy Volcano
Arc magmas are generated by a number of mantle and
crustal processes. Our multidisciplinary, long-term research is
aimed at deciphering these processes for a single arc volcano,
Kliuchevskoy volcano in Kamchatka. Some key results of the
study follow:
1) Modeling of trace element and H2O contents in melt
inclusions suggests that the primary magmas originate via
hydrous flux-melting of the mantle wedge at temperatures
close to the dry peridotite solidus. The role of decompression
melting is minor or absent at Kliuchevskoy and other arc
volcanoes built on relatively thick crust.
2) Geochemistry of high-Mg olivine suggests that primary
Kliuchevskoy magmas have substantial contribution from
olivine-free pyroxenite (up to 30 %), which could be formed
by reaction of slab melts (or supercritical fluids) with mantle
wedge peridotite.
3) Parental Kliuchevskoy melts start to crystallize as deep
as the Moho boundary, and the erupted magmas reflect multistage
and complex processes of crystallization, magma mixing
and crustal assimilation. None of the Kliuchevskoy rocks
analyzed thus far represent true primary melt compositions.
4) The Kliuchevskoy Holocene eruptive history is not
steady-state in terms of eruption rate and geochemistry. There
are two millenial cycles with major and trace element and OSr-
Nd-Pb and U-series isotope compositions of the magmas
changing gradually from more to less affected by crustal (?)
assimilation. The onset of the cycles correlates with periods of
enhanced volcanic activity in Kamchatka, suggesting that the
extent of magma-crust interaction is inversely related to
magma production rate and thus magma flux from the mantle
Persistent spin textures in halide perovskites induced by uniaxial stress
Persistent spin textures are highly desirable for applications in spintronics
as they may allow for long carrier spin lifetimes. However, they are also rare
as only four point groups can host such textures, and even for these four
groups, the emergence of persistent spin textures requires a delicate balance
between coupling parameters, which control the strength of spin-momentum
interactions. We use first-principles density functional simulations to predict
the possibility of achieving these desirable spin textures through the
application of uniaxial stress. Hybrid organic-inorganic perovskite MPSnBr
(MP = CHPH) is a ferroelectric semiconductor which exhibits persistent
spin textures in the near to its conduction band minimum and mostly Rashba type
in the vicinity of its valence band maximum. Application of uniaxial stress
leads to the gradual evolution of the valence bands spin textures from mostly
Rashba type to persistent ones under tensile load and to pure Rashba or
persistent ones under compressive load. We also report that the material
exhibits flexibility, rubber-like response, and both positive and negative
piezoelectric constants. Combination of such properties may create
opportunities for a flexible/rubbery spintronic devices
Multi-Cyclic and Isotopically Diverse Silicic Magma Generation in an Arc Volcano: Gorely Eruptive Center, Kamchatka, Russia
The Kamchatka Peninsula is home to some of the most frequent and prolific subduction-related volcanic activity in the world, with the largest number of caldera-forming eruptions per length of the volcanic arc. Among those, Gorely volcano has a topographically prominent Late Pleistocene caldera (13 km × 12 km, estimated to have produced >100 km3 of magma), which is now almost completely filled by a central cone. We report new 40Ar/39Ar ages and geochemical and isotopic data for newly recognized Mid-Pleistocene ignimbrite units of large but unknown volume sourced from the Gorely eruptive center, most of which were deposited in marginal glacial conditions. These ignimbrites have crystallinities of 9-24% and most are quartz-, amphibole-, and zircon-undersaturated. Additionally, we studied 32 eruptive units, including stratigraphically constrained Holocene tephra, and pre- and post-caldera lava sequences, to understand the petrogenetic and temporal evolution of this long-lived, multi-cyclic, arc volcano. Material erupted prior to the formation of the modern Gorely edifice, including the voluminous ignimbrites and eruptions of the ‘pra-Gorely' stage, consist primarily of dacite and andesite, whereas sequences of the modern Gorely edifice are represented by basalt to basaltic andesite. MELTS and EC-AFC modeling shows that it is possible to obtain silicic compositions near those of the evolved ignimbrite compositions through 60-75% fractional crystallization at 1 kbar and nickel-nickel oxide (NNO) oxygen fugacity. However, our newly compiled major and trace element data for Gorely yield two separate bimodal peaks in a SiO2-frequency diagram, showing a prominent Daly Gap, with a deficiency in andesite. Trace element concentrations define two separate trends, one for more silicic and another for more mafic sequences. Additionally, δ18Omelt values reconstructed from coexisting plagioclase and clinopyroxene phenocrysts range from a low value of 4·85‰ to a normal value of 6·22‰. The low δ18O values range throughout the known lifespan of Gorely, with the lowest value being from the first known ignimbrite to erupt, indicating episodic but temporally decreasing crustal assimilation of previously hydrothermally altered material. 87Sr/86Sr and 143Nd/144Nd ratios show wide ranges from 0·70328 to 0·70351 and from 0·51303 to 0·51309 respectively, also suggesting incorporation of surrounding crust, although there are less clear trends throughout the lifespan of Gorely. The combination of light and diverse δ18O values with elevated 87Sr/86Sr and low 143Nd/144Nd ratios suggests contamination by older and isotopically diverse, low-δ18O country-rocks, such as the neighboring 11 Ma Akhomten granitic massif, which shows ranges in δ18O, 87Sr/86Sr, and 144Nd/143Nd values overlapping with the Gorely magmas. In addition, the presence of glomerocrysts and mafic enclaves in the majority of Gorely dacites indicates a period of crystal settling and subsequent intrusion of hot, primitive basalt that probably triggered eruption. Finally, elevated Nb concentrations relative to other Kamchatkan volcanoes suggest that Gorely magmas may involve an enriched component, probably caused by delamination of a lower crustal root. Our results argue for an incremental view of silicic magma generation at so-called ‘long-term eruptive centers', in Kamchatka and worldwide, consisting of alternating episodes of magmatic and hydrothermal activity, and glacial advances and retreats. We demonstrate that large-volume, isotopically distinct, silicic magma can be generated rapidly between cone-building phases of volcanic activity through a combination of fractional crystallization, assimilation of older country rocks, and shallow assimilation of hydrothermally altered but otherwise petrochemically similar older intracaldera tuffs and intrusions. These transient shallow silicic magma chambers empty nearly completely in ignimbrite-forming eruptions after 103-105 years of assembly, partially triggered by glacial surface dynamic
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