127 research outputs found
Vibrational properties of alpha- and sigma-phase Fe-Cr alloy
Experimental investigation as well as theoretical calculations, of the
Fe-partial phonon density-of-states (DOS) for nominally Fe_52.5Cr_47.5 alloy
having (a) alpha- and (b) sigma-phase structure were carried out. The former at
sector 3-ID of the Advanced Photon Source, using the method of nuclear resonant
inelastic X-ray scattering, and the latter with the direct method [K. Parlinski
et al., Phys. Rev. Lett. {78, 4063 (1997)]. The characteristic features of
phonon DOS, which differentiate one phase from the other, were revealed and
successfully reproduced by the theory. Various data pertinent to the dynamics
such as Lamb-Mossbauer factor, f, kinetic energy per atom, E_k, and the mean
force constant, D, were directly derived from the experiment and the
theoretical calculations, while vibrational specific heat at constant volume,
C_V, and vibrational entropy, S were calculated using the Fe-partial DOS. Using
the values of f and C_V, we determined values for Debye temperatures, T_D. An
excellent agreement for some quantities derived from experiment and
first-principles theory, like C_V and quite good one for others like D and S
was obtained.Comment: 4 pages, 3 figure
ОЦЕНКА СТАВОК АРЕНДЫ КОММЕРЧЕСКОЙ НЕДВИЖИМОСТИ НА УЗКИХ РЫНКАХ
The narrow markets in small settlements where the commercial real estate supply is scarce cannot be analyzed statistically. The problem becomes extremely complex when the research should take into consideration a wide range of Russian settlements. Moreover, there is a mismatch between the expected labor costs for data collecting and processing and achieved results.In this context, the task of developing a methodology for determining the rental rates for commercial real estate in the narrow markets in conditions of zero or minimum supply is highly relevant. The article shows that the main problem is to find correlation between economically reasonable and statistically proven average rental rates and a straightforward factor which can be easily determined. Узкие рынки аренды коммерческой недвижимости в малых населенных пунктах, где предложение на рынке содержит единичные помещения, не поддаются статистическому анализу. Особо обостряется данная проблема при необходимости охвата широкого перечня населенных пунктов России. Кроме того, возникает проблема несоответствия между ожидаемыми трудозатратами на сбор и обработку данных и достигаемыми результатами. В связи с этим актуальна задача разработки методики определения ставок аренды коммерческой недвижимости на узких рынках при отсутствующем или минимальном предложении. Идея методики состоит в поиске экономически обоснованной и статистически подтвержденной связи средних по городу ставок аренды с фактором, определение которого не вызывает затруднений, что и показано в данной статье.
Investigation of surface structure, electrokinetic and stability properties of highly dispersed Ho₂O₃-Yb₂O₃/SiO₂ nanocomposites
A series of highly dispersed Ho2O3–Yb2O3/SiO2 nanocomposites was synthesized using a liquid-phase method and examined using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), nitrogen adsorption–desorption, transmission electron microscopy (TEM), Scanning Electron Microscopy (SEM), and photon correlation spectroscopy (PCS). X-ray fluorescence spectrometry (XRF) confirmed a similar amount of weight percentage of Ho, Yb and Si oxides in the prepared samples. Samples HoYbSi1 (Ho2O3:Yb2O3:SiO2 = 0.5:10:89.5, wt. %), HoYbSi2 (Ho2O3:Yb2O3:SiO2 = 1:10:89, wt. %) and HoYbSi3 (Ho2O3:Yb2O3:SiO2 = 2:10:88, wt. %) calcined at 550 °C are amorphous. TEM and SEM analysis confirm a sphere-like morphology with a quite homogeneous size and shape. As compared with the initial silica, the agglomerated particles of nanocomposites in the aqueous medium are in the range from 200 to 850 nm according to PCS data. The effect of anionic polyacrylic acid (PAA) adsorption on fumed silica (SiO2) and Ho2O3–Yb2O3/SiO2 nanocomposite surfaces on suspension stability was studied. The turbidymetry method was used to monitor the initial silica and triple nanooxides suspensions stability as a function of time
Superconductivity of Mo3Sb7 from first principles
Superconductivity in Mo3Sb7 is analyzed using the combined electronic
structure and phonon calculations, and the electron--phonon coupling constant
\lambda_{ph}=0.54 is determined from first principles. This value explains the
experimental value of the superconducting critical temperature T_c=2.2 K. The
possible influence of spin fluctuations and spin gap on the superconductivity
in Mo3Sb7 is discussed, and electron--paramagnon interaction is found to be
weak.Comment: 4 pages, 4 figures. To be published in Phys. Rev.
Structure and elastic properties of Mg(OH) from density functional theory
The structure, lattice dynamics and mechanical properties of the magnesium
hydroxide have been investigated with static density functional theory
calculations as well as \it {ab initio} molecular dynamics. The hypothesis of a
superstructure existing in the lattice formed by the hydrogen atoms has been
tested. The elastic constants of the material have been calculated with static
deformations approach and are in fair agreement with the experimental data. The
hydrogen subsystem structure exhibits signs of disordered behaviour while
maintaining correlations between angular positions of neighbouring atoms. We
establish that the essential angular correlations between hydrogen positions
are maintained to the temperature of at least 150 K and show that they are well
described by a physically motivated probabilistic model. The rotational degree
of freedom appears to be decoupled from the lattice directions above 30K
Origin of monoclinic distortion and its impact on the electronic properties in KO
We use the density functional theory and lattice dynamics calculations to
investigate the properties of potassium superoxide KO in which spin,
orbital, and lattice degrees of freedom are interrelated and determine the
low-temperature phase. After calculating phonon dispersion relations in the
high-temperature tetragonal structure, we identify a soft phonon mode
leading to the monoclinic symmetry and optimize the crystal geometry
resulting from this mode. Thus we reveal a displacive character of the
structural transition with the group-subgroup relation between the tetragonal
and monoclinic phases. We compare the electronic structure of KO with
antiferromagnetic spin order in the tetragonal and monoclinic phases. We
emphasize that realistic treatment of the electronic structure requires
including the local Coulomb interaction in the valence orbitals of the
O ions. The presence of the `Hubbard' leads to the gap opening at the
Fermi energy in the tetragonal structure without orbital order but with weak
spin-orbit interaction. We remark that the gap opening in the tetragonal phase
could also be obtained when the orbital order is initiated in the calculations
with a realistic value of . Finally, we show that the local Coulomb
interactions and the finite lattice distortion, which together lead to the
orbital order via the Jahn-Teller effect, are responsible for the enhanced
insulating gap in the monoclinic structure.Comment: accepted by Physical Review
Ab initio and nuclear inelastic scattering studies of FeSi/GaAs heterostructures
The structure and dynamical properties of the FeSi/GaAs(001) interface
are investigated by density functional theory and nuclear inelastic scattering
measurements. The stability of four different atomic configurations of the
FeSi/GaAs multilayers is analyzed by calculating the formation energies and
phonon dispersion curves. The differences in charge density, magnetization, and
electronic density of states between the configurations are examined. Our
calculations unveil that magnetic moments of the Fe atoms tend to align in a
plane parallel to the interface, along the [110] direction of the FeSi
crystallographic unit cell. In some configurations, the spin polarization of
interface layers is larger than that of bulk FeSi. The effect of the
interface on element-specific and layer-resolved phonon density of states is
discussed. The Fe-partial phonon density of states measured for the FeSi
layer thickness of three monolayers is compared with theoretical results
obtained for each interface atomic configuration. The best agreement is found
for one of the configurations with a mixed Fe-Si interface layer, which
reproduces the anomalous enhancement of the phonon density of states below 10
meVComment: 14 pages, 9 figures, 4 table
The expression of B7-H1 and B7-H4 molecules on immature myeloid and lymphoid dendritic cells in cord blood of healthy neonates.
The aim of our study was to estimate both B7-H1 and B7-H4 molecules on immature myeloid and lymphoid dendritic cells in umbilical cord blood of healthy neonates in comparison with peripheral blood of healthy adults. Thirty nine healthy full-term neonates from physiological single pregnancies and 27 healthy adults were included in the study. The expression of B7-H1 and B7-H4 was revealed using the immunofluorescence method. Statistical analysis was performed using a non-parametric test (Mann-Whitney U-Test). The percentages of BDCA-1+ dendritic cells with B7-H1 and B7-H4 expressions were significantly higher in peripheral blood of healthy adults (
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