289 research outputs found
The variation of the magnetic field of the Ap star HD~50169 over its 29 year rotation period
Context. The Ap stars that rotate extremely slowly, with periods of decades
to centuries, represent one of the keys to the understanding of the processes
leading to the differentiation of stellar rotation.
Aims. We characterise the variations of the magnetic field of the Ap star HD
50169 and derive constraints about its structure.
Methods. We combine published measurements of the mean longitudinal field
of HD 50169 with new determinations of this field moment from circular
spectropolarimetry obtained at the 6-m telescope BTA of the Special
Astrophysical Observatory of the Russian Academy of Sciences. For the mean
magnetic field modulus , literature data are complemented by the analysis of
ESO spectra, both newly acquired and from the archive. Radial velocities are
also obtained from these spectra.
Results. We present the first determination of the rotation period of HD
50169, Prot = (29.04+/-0.82) y. HD 50169 is currently the longest-period Ap
star for which magnetic field measurements have been obtained over more than a
full cycle. The variation curves of both and have a significant degree
of anharmonicity, and there is a definite phase shift between their respective
extrema. We confirm that HD 50169 is a wide spectroscopic binary, refine its
orbital elements, and suggest that the secondary is probably a dwarf star of
spectral type M.
Conclusions. The shapes and mutual phase shifts of the derived magnetic
variation curves unquestionably indicate that the magnetic field of HD 50169 is
not symmetric about an axis passing through its centre. Overall, HD 50169
appears similar to the bulk of the long-period Ap stars.Comment: 10 pages, 3 figures, accepted for publication in A&
Complex Estimation of Physical Capacity of Volley-Ballers.
У статті висвітлено особливості прояву фізичної працездатності юнаків і дівчат-волейболістів. На основі встановлених кількісних величин фізичної працездатності розроблено нормативи її комплексної оцінки. The
features of display of physical capacity and girls of volley-ballers youth are reflected in the article. On the basis of the
set quantitative sizes of physical capacity the norms of its complex estimation are developed
Possible detection of a magnetic field in T Tauri
Medium-resolution circular spectropolarimetry of T Tauri is
presented. The star was observed twice: on November 11, 1996 and January 22,
2002. Weak circular polarization has been found in photospheric absorption
lines, indicating a mean surface longitudinal magnetic field of
G and G at the epoch of the first and second
observations respectively. While these values are near the detection limit of
our apparatus, we belive that they are real. In any case one can conclude from
our data that of T Tau does not significantly exceed 200 G, which is
much less than surface magnetic field strength of the star ( kG) found by
Guenther et al. (1999) and Johns-Krull et al. (2000). We discuss possible
reasons of this difference.Comment: 5 pages, 3 figure
Photoemission study and band alignment of GaN passivation layers on GaInP heterointerface
III-V semiconductor-based photoelectrochemical (PEC) devices show the highest
solar-to-electricity or solar-to-fuel conversion efficiencies. GaInP is a
relevant top photoabsorber layer or a charge-selective contact in PEC for
integrated and direct solar fuel production, due to its tunable lattice
constant, electronic band structure, and favorable optical properties. To
enhance the stability of its surface against chemical corrosion which leads to
decomposition, we deposit a GaN protection and passivation layer. The n-doped
GaInP(100) epitaxial layers were grown by metalorganic chemical vapor
deposition on top of GaAs(100) substrate. Subsequently, thin 1-20 nm GaN films
were grown on top of the oxidized GaInP surfaces by atomic layer deposition. We
studied the band alignment of these multi-junction heterostructures by X-ray
and ultraviolet photoelectron spectroscopy. Due to the limited emission depth
of photoelectrons, we determined the band alignment by a series of separate
measurements in which we either modified the GaInP(100) surface termination or
the film thickness of the grown GaN on GaInP(100) buffer layers. On
n-GaInP(100) surfaces prepared with the well-known phosphorus-rich (2x2)/c(4x2)
reconstruction we found up-ward surface band bending (BB) of 0.34 eV, and Fermi
level pinning due to the present surface states. Upon oxidation, the surface
states are partially passivated resulting in a reduction of BB to 0.12 eV and a
valence band offset (VBO) between GaInP and oxide bands of 2.0 eV. Between the
GaInP(100) buffer layer and the GaN passivation layer, we identified a VBO of
1.8 eV. The corresponding conduction band offset of -0.2 eV is found to be
rather small. Therefore, we evaluate the application of the GaN passivation
layer as a promising technological step not only to reduce surface states but
also to increase the stability of the surfaces of photoelectrochemical devices
HD 965: An extremely peculiar A star with an extremely long rotation period
Context. One of the keys to understanding the origin of the Ap stars and
their significance in the general context of stellar astrophysics is the
consideration of the most extreme properties displayed by some of them. In that
context, HD 965 is particularly interesting, as it combines some of the most
pronounced chemical peculiarities with one of the longest rotation periods
known.
Aims. We characterise the variations of the magnetic field of the Ap star HD
965 and derive constraints about its structure.
Methods. We combine published measurements of the mean longitudinal field
of HD 965 with new determinations of this field moment from circular
spectropolarimetry obtained at the 6-m telescope BTA of the Special
Astrophysical Observatory of the Russian Academy of Sciences. For the mean
magnetic field modulus , literature data are complemented by the analysis of
ESO archive spectra.
Results. We present the first determination of the rotation period of HD 965,
P = (16.5+/-0.5) y. HD 965 is only the third Ap star with a period longer than
10 years for which magnetic field measurements have been obtained over more
than a full cycle. The variation curve of is well approximated by a cosine
wave. does not show any significant variation. The observed behaviour of
these field moments is well represented by a simple model consisting of the
superposition of collinear dipole, quadrupole and octupole. The distribution of
neodymium over the surface of HD 965 is highly non-uniform. The element appears
concentrated around the magnetic poles, especially the negative one.
Conclusions. The shape of the longitudinal magnetic variation curve of HD 965
indicates that its magnetic field is essentially symmetric about an axis
passing through the centre of the star. Overall, as far as its magnetic field
is concerned, HD 965 appears similar to the bulk of the long-period Ap stars.Comment: 7 pages, 4 figures, accepted for publication in Astronomy &
Astrophysics. arXiv admin note: text overlap with arXiv:1902.0586
Time resolved in situ spectroscopy during formation of the GaP Si 100 heterointerface
Though III V Si 100 heterointerfaces are essential for future epitaxial high performance devices, their atomic structure is an open historical question. Benchmarking of transient optical in situ spectroscopy during chemical vapor deposition to chemical analysis by X ray photoelectron spectroscopy enables us to distinguish between formation of surfaces and of the heterointerface. A terrace related optical anisotropy signal evolves during pulsed GaP nucleation on single domain Si 100 surfaces. This dielectric anisotropy agrees well with the one calculated for buried GaP Si 100 interfaces from differently thick GaP epilayers. X ray photoelectron spectroscopy reveals a chemically shifted contribution of the P and Si emission lines, which quantitatively corresponds to one monolayer and establishes simultaneously with the nucleation related optical in situ signal. We attribute that contribution to the existence of Si P bonds at the buried heterointerface. During further pulsing and annealing in phosphorus ambient, dielectric anisotropies known from atomically well ordered GaP 100 surfaces super impose the nucleation related optical in situ spectra. Figure Presente
Electrodialysis Concentration of Sulfuric Acid
Received: 31.12.2020. Revised: 30.03.2021. Accepted: 30.03.2021. Available online: 31.03.2021.This article belongs to the PCEE-2020 Special Issue.An urgent task is the development of new resource-saving technologies for deep processing of wastes from the hydrometallurgical industry for the purpose of their reuse. Membrane technologies make it possible to create closed technological cycles with the reuse of recovered components in production, which allows solving many environmental problems. At the Abinsk Electric Steel Works Ltd. (Russia), during the production of copper-coated steel wire, a large amount of waste containing sulfuric acid and heavy metal salts is generated. The chemical treatment of such effluents with slaked lime and alkali produces a large amount of sludge, which causes environmental problems and leads to the irreversible loss of sulfuric acid. The problem of separating acids and salts can be solved using diffusion dialysis through anion-exchange membranes, however, to return the acid to the production cycle, the purified acid must be additionally concentrated. In this work, we studied the process of electrodialysis concentration of sulfuric acid using heterogeneous ion-exchange membranes Ralex® CMHPP and Ralex® AMHPP (manufactured by MEGA a.s., Czech Republic) which have a polypropylene reinforcing mesh resistant to acids. The main parameters of the electrodialysis concentration process have been determined – the dependence of the concentration of the regenerated sulfuric acid on the concentration at the inlet to the electrodialysis cell and on the current density, as well as the energy consumption for the process. It is shown that with the help of electrodialysis concentration it is possible to obtain sulfuric acid with a concentration of up to 180 g/L, which makes it possible to return it to the production cycle.This study was funded by the Ministry of Education and Science of the Russian Federation (project No. FZEN-2020-0022)
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