487 research outputs found
Surface reactions with participation of oxides of molybdenum and tungsten
The kinetics of surface reactions in one-dimensional and radial (two-dimensional) distribution of diffusant MoO3 (WO3) on the surface of the substrate MeO (Me is Cd, Ni, Pb, Mn, Cu) were investigated. A kinetic equation satisfactorily describes the rate
of surface reactions in the case of radial distribution of diffusant on the substrate. It’s found that when the radial distribution of diffusant the growth of layer on the substrate surface eventually slows down and stops almost completely, due to the outflow of the diffusant deeps into the substrate. When the one-dimensional distribution of diffusant the surface interaction is not slowed down and does not stop at an arbitrarily large times
Surface reactions with participation of oxides of molybdenum and tungsten: the influence of external factors
This work is a continuation of the article “Surface reactions with participation of oxides of molybdenum and tungsten”, published in the previous issue of the journal. The influence of the electric field and the pressure of oxygen in the gas phase on the rate of surface reactions for the synthesis of molybdates of manganese and copper were investigated. It’s found that for the synthesis reaction of molybdate of copper the nature of the dependency of the rate of synthesis and rate of surface reactions from the external parameters are the same, indicating the crucial contribution of surface diffusion to the reactive mass transfer. For the synthesis reaction of molybdate of manganese the dependences of the rate of synthesis and of rate of surface reactions by external parameters differ, indicating that for this reaction, surface diffusion isn’t the main mechanism of mass transfer
Murina Galina-Vanzetti Vasiliyevna: biobibliographic profile
This issue is a humble contribution to celebration of the 85-th birthday of Galina-Vanzetti V. Murina, D.Sc. (Biol.), Professor, the recognized authority in the taxonomy and zoogeography of mariculture organisms and meroplankton. For several decades Dr. G.-V.V. Murina has been a leading scientific worker at the Department of Mariculture and Applied Oceanology in the Institute of Biology of the Southern Seas, the National Academy of Sciences of Ukraine. The key points of her biography and scientific advancement are presented. This publication is intended for biologists, oceanologists, zoologists, ecologists, post graduates, university students and for any interested reader
Transport properties of the azimuthal magnetorotational instability
The magnetorotational instability (MRI) is thought to be a powerful source of turbulence in Keplerian
accretion disks. Motivated by recent laboratory experiments, we study the MRI driven by an azimuthal
magnetic field in an electrically conducting fluid sheared between two concentric rotating cylinders.
By adjusting the rotation rates of the cylinders, we approximate angular velocity profiles ω ∝ r
q
. We
perform direct numerical simulations of a steep profile close to the Rayleigh line q & −2 and a quasiKeplerian
profile q ≈ −3/2 and cover wide ranges of Reynolds (Re ≤ 4 · 104
) and magnetic Prandtl
numbers (0 ≤ Pm ≤ 1). In the quasi-Keplerian case, the onset of instability depends on the magnetic
Reynolds number, with Rmc ≈ 50, and angular momentum transport scales as √
PmRe2
in the turbulent
regime. The ratio of Maxwell to Reynolds stresses is set by Rm. At the onset of instability both
stresses have similar magnitude, whereas the Reynolds stress vanishes or becomes even negative as
Rm increases. For the profile close to the Rayleigh line, the instability shares these properties as long
as Pm & 0.1, but exhibits a markedly different character if Pm → 0, where the onset of instability is
governed by the Reynolds number, with Rec ≈ 1250, transport is via Reynolds stresses and scales as
Re2
. At intermediate Pm = 0.01 we observe a continuous transition from one regime to the other, with
a crossover at Rm = O(100). Our results give a comprehensive picture of angular momentum transport
of the MRI with an imposed azimuthal field
The blue compact dwarf galaxy I Zw 18: a comparative study of its low-surface-brightness component
(abridged): Using HST and ground-based optical and NIR imaging data, we
investigate whether the blue compact dwarf (BCD) galaxy I Zw 18 possesses an
extended low-surface-brightness (LSB) old stellar population underlying its
star-forming (SF) regions. We show that the exponential intensity decrease
observed in the filamentary LSB envelope of the BCD out to 18 arcsec (1.3 kpc
at a distance of 15 Mpc) is not due to an evolved stellar disc, but rather due
to extended ionized gas emission. Broad-band images reveal, after subtraction
of nebular line emission, a compact stellar LSB component extending slightly
beyond the SF regions. This stellar host, being blue over a radius range of 5
exponential scale lengths and showing little colour contrast to the SF
component, differs strikingly from the red LSB host of standard BCDs. This
fact, in connection with the blue colors of component I Zw 18 C, suggests that
most of the stellar mass in I Zw 18 has formed within the last 0.5 Gyr.
Furthermore, we show that the exponential intensity fall-off in the filamentary
ionized envelope of I Zw 18 is not particular to this system but a common
property of the ionized halo of many SF dwarf galaxies on galactocentric
distances of several kpc. In the absence of an appreciable underlying stellar
background, extended ionized gas emission dominates in the periphery of I Zw
18, mimicking an exponential stellar disc on optical surface brightness
profiles.Comment: 24 pages, 16 figures; accepted for publication in Astronomy &
Astrophysics; higher resolution images available at
http://alpha.uni-sw.gwdg.de/~papade/IZw18
Correlation between local slip rate and local high-frequency radiation capability in a hearthquake fault
Training in physical education of preschool children
Представлен опыт физкультурной и оздоровительной работы в детском саду, показаны методы повышения мотивации детей к спортивным занятиям, методы воспитания чувства коллективизма, активности, инициативности, настойчивости, смелости, выдержки и сознательной дисциплинированностиDescribes the experience of physical exercise and fitness work in the kindergarten, demonstrate how to motivate children towards sporting activities, methods of education a sense of community, activity, initiative, perseverance, courage, endurance and conscious disciplin
A spectroscopic study of component C and the extended emission around I Zw 18
Long-slit Keck II, 4m Kitt Peak, and 4.5m MMT spectrophotometric data are
used to investigate the stellar population and the evolutionary status of I Zw
18C, the faint C component of the nearby blue compact dwarf galaxy I Zw 18.
Hydrogen H and H emission lines are detected in the spectra of I
Zw 18C, implying that ionizing massive stars are present. High signal-to-noise
Keck II spectra of different regions in I Zw 18C reveal H, H
and higher order hydrogen lines in absorption. Several techniques are used to
constrain the age of the stellar population in I Zw 18C. Ages derived from two
different methods, one based on the equivalent widths of the H,
H emission lines and the other on H, H absorption lines
are consistent with a 15 Myr instantaneous burst model. We find that a small
extinction in the range = 0.20 -- 0.65 mag is needed to fit the observed
spectral energy distribution of I Zw 18C with that model. In the case of
constant star formation, all observed properties are consistent with stars
forming continuously between ~ 10 Myr and < 100 Myr ago. We use all available
observational constraints for I Zw 18C, including those obtained from Hubble
Space Telescope color-magnitude diagrams, to argue that the distance to I Zw 18
should be as high as ~ 15 Mpc. The deep spectra also reveal extended ionized
gas emission around I Zw 18. H emission is detected as far as 30" from
it. To a B surface brightness limit of ~ 27 mag arcsec we find no
observational evidence for extended stellar emission in the outermost regions,
at distances > 15" from I Zw 18.Comment: 38 pages, 11 Postscript figures, accepted for publication in the
Astrophysical Journa
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