2,006 research outputs found
Preparation and characterization of Bi26–2xMn2xMo10O69-d and Bi26.4Mn0.6Mo10–2yMe2yO69-d(Me = V, Fe) solid solutions
Received: 06.06.2017; accepted: 23.06.2017; published: 14.07.2017.Single phase samples of bismuth molybdate, Bi26Mo10O69, doped with Mn on the bismuth sublattice and V, Fe on the molybdenum sublattice were found to crystallize in the triclinic Bi26Mo10O69 structure at low doping levels and in the monoclinic Bi26Mo10O69 structure - at higher dopant concentration. The assumption that all Mn ions have an oxidation state of +2 was confirmed by means of magnetic measurement results analysis using Curie-Weiss law. Conductivity was investigated using impedance spectroscopy. The conductivity of Bi26.4Mn0.6Mo9.6Fe0.4O69-d was 1.2*10-2 S*cm-1 at 973 K and 2.2*10-4 S*cm-1 at 623 K, and the conductivity of Bi26.4Mn0.6Mo9.2V0.8O69-d was 2.2*10-3 S*cm-1 at 973 K and 2.2*10-5 S*cm-1 at 623 K
NMR and LDA evidence for spiral magnetic order in the chain cuprate LiCu2O2
We report on {6,7}Li nuclear magnetic resonance measurements of the
spin-chain compound LiCu2O2 in the paramagnetic and magnetically ordered
states. Below T about 24 K the NMR lineshape presents a clear signature of
incommensurate (IC) static modulation of the local magnetic field consistent
with an IC spiral modulation of the magnetic moments. {7}Li NMR reveals strong
phason-like dynamical fluctuations extending well below 24 K. We hypothesize
that a series of phase transitions at 24.2, 22.5, and 9 K reflects a "Devil's
staircase" type behavior generic for IC systems. LDA based calculations of
exchange integrals reveal a large in-chain frustration leading to a magnetical
spiral.Comment: 4 pages, 4 figure
Crystal structure and conductivity of bismuth-containing complex oxides
In the paper, a comprehensive systematic study of different classes of bismuth containing oxide compounds was carried out. The relationship between composition, temperature and concentration regions of existence of stable, specific structure and properties of solid solutions on the basis of vanadates, molybdates, niobates and bismuth was found. The general regularities of synthesis of solid solutions with different variants of solid-phase and soluble methods were determined. On this basis, the optimal conditions for obtaining
single-phase materials were formulated. For the first time the temperature and concentration boundaries of the regions of homogeneity and areas of stable existence of polymorphic modifications of solid solutions were defined and/or refined. The structural parameters of the synthesized phases were determined. By the method of electrochemical impedance spectroscopy the nature and features
of impedance spectra, the temperature and concentration dependences of electrical conductivity of ceramic materials based on bismuth containing complex oxides were identified
Correction of artificial jumps in the historical geomagnetic measurements of Coimbra Observatory, Portugal
The Coimbra Magnetic Observatory (International Association of Geomagnetism and Aeronomy code COI) in Portugal has a long
history of observation of the geomagnetic field, spanning almost 150 yr
since the first geomagnetic measurements in 1866. These long instrumental
geomagnetic records provide very important information about variability of
geomagnetic elements and indices, their trends and cycles, and can be used
to improve our knowledge on the sources that drive variations of the
geomagnetic field: liquid core dynamics (internal) and solar forcing
(external).
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However, during the long life of the Coimbra Observatory, some inevitable
changes in station location, instrument's park and electromagnetic
environment have taken place. These changes affected the quality of the data
collected at COI causing breaks and jumps in the series of geomagnetic field
components and local K index. Clearly, these inhomogeneities, typically
shift-like (step-like) or trend-like, have to be corrected or, at least,
minimized in order for the data to be used in scientific studies or to be
submitted to international databases.
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In this study, the series of local K index and declination of the
geomagnetic field are analysed: the former because it allows direct
application of standard homogenization methods and the latter because it is
the longest continuous series produced at COI. For the homogenization,
visual and statistical tests (e.g. standard normal homogeneity test) have
been applied directly to the local geomagnetic K index series (from 1951 to
2012). The homogenization of the monthly averages of declination (from 1867
to 2012) has been done using visual analysis and statistical tests applied
to the time series of the first differences of declination values, as an
approximation to the first time derivative. This allowed not only
estimating the level of inhomogeneity of the studied series but also
detecting the highly probable homogeneity break points. These points have been
cross-checked with the metadata, and the COI series have been compared with
reference series from the nearest geomagnetic stations and, in the case of
declination series, from the recent geomagnetic field model COV-OBS to set
up the required correction factors. As a result, the homogenized series
measured in COI are considered to be essentially free of artificial shifts
starting from the second half of the 20th century, and ready to be used by
the scientific community
Grain sizes and dislocation densities in fcc-metallic materials processed by warm to hot working
Our just received results on the deformation microstructures evolved in a mediumMn austenitic steel during large strain warm to hot rolling were analyzed with a reference to other alloys with face centred cubic lattices and relatively low stacking fault energies. The structural changes were characterized by the development of dynamic recovery (DRV) and dynamic recrystallization (DRX). The deformation grain size decreased while the dislocation density increased with a decrease in deformation temperatur
The - divergence and Mixing times of quantum Markov processes
We introduce quantum versions of the -divergence, provide a detailed
analysis of their properties, and apply them in the investigation of mixing
times of quantum Markov processes. An approach similar to the one presented in
[1-3] for classical Markov chains is taken to bound the trace-distance from the
steady state of a quantum processes. A strict spectral bound to the convergence
rate can be given for time-discrete as well as for time-continuous quantum
Markov processes. Furthermore the contractive behavior of the
-divergence under the action of a completely positive map is
investigated and contrasted to the contraction of the trace norm. In this
context we analyse different versions of quantum detailed balance and, finally,
give a geometric conductance bound to the convergence rate for unital quantum
Markov processes
Influence of thiamine injections on the folic acid balance in white rats organism
The interaction of thiamine and folic acid in the organism of white rats were carried out under intramuscular injections of thiamine. The research was conducted on 120 white Wistar rats weighing 150-200 g, which were divided into two groups, one was injected with thiamine, and the second was a control group. All animals were obtained the standard ration of the vivarium.After intramuscular injections of thiamine in dose 1 mg/kg mass it was established, that folic acid content after 60-240 min after injection decrease in small intestine and muscles of animals. Meanwhile, this indication in liver and blood increased.These data achieve that thiamine injection leads to changes of folic acid content in different tissue
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