209 research outputs found
Analysis of the spectral energy distribution of the coolest RCrB type carbon star DY Per
We analyse the spectral energy distribution of the evolved carbon giant DY
Per with a spectral synthesis technique. The red giant shows the photometric
features of R CrB type stars. We derive the atmospheric parameters of DY Per
using three variants of molecular line lists. We estimate Teff to be in the
range 2900 < Teff < 3300 K. We adopted log g = 0. The star may be metal
deficient and hydrogen deficient. The maximum possible carbon abundance in the
star, [C]=0.94, provides the following atmospheric parameters: Tef=3100 K,
[Fe/H] = 0, log(C/O)=0.6, [N/Fe] = 0, [H/He] = 0, with Jorgensen's line lists
for the molecules C2 and CN.Comment: 4 pages, 2 tables, 3 figs, accepted by Odessa asronomical observatory
Publ., 200
The Ever Changing Circumstellar Nebula Around UW Centauri
We present new images of the reflection nebula surrounding the R Coronae
Borealis Star, UW Cen. This nebula, first detected in 1990, has changed its
appearance significantly. At the estimated distance of UW Cen, this nebula is
approximately 0.6 ly in radius so the nebula cannot have physically altered in
only 8 years. Instead, the morphology of the nebula appears to change as
different parts are illuminated by light from the central star modulated by
shifting thick dust clouds near its surface. These dust clouds form and
dissipate at irregular intervals causing the well-known declines in the R
Coronae Borealis (RCB) stars. In this way, the central star acts like a
lighthouse shining through holes in the dust clouds and lighting up different
portions of the nebula. The existence of this nebula provides clues to the
evolutionary history of RCB stars possibly linking them to the Planetary
Nebulae and the final helium shell flash stars.Comment: To be published in ApJ Letters. 5 pages, 3 figures (2 in color
TRAINING OF PEDAGOGICAL EDUCATION MASTERS: PRACTICE-ORIENTED MODEL
Purpose: The article deals with the problems of training, attraction, and retention of teachers of the required qualification in educational institutions.
Methodology: This problem is analyzed at the regional level in the context of reforms in the higher education system, the transition to a two-level model in accordance with the provisions of the Bologna process.
Result: Based on the analysis of open data in the work it is stated that the shortage of teachers in the region (Samara region) is significant and has a negative impact on the educational process of educational institutions; it cannot be compensated exclusively by bachelors of pedagogical education, issued by pedagogical universities.
Applications: This research can be used for universities, teachers, and students.
Novelty/Originality: In this research, the model of training of pedagogical education masters: practice-oriented model is presented in a comprehensive and complete manner
Spectropolarimetry of R Coronae Borealis in 1998--2003: Discovery of Transient Polarization at Maximum Brightness
We present an extended optical spectropolarimetry of R CrB from 1998 January
to 2003 September. The polarization was almost constant in the phase of maximum
brightness, being consistent with past observations. We detected, however,
temporal changes of polarization ( %) in 2001 March and August, which
were the first detection of large polarization variability in R CrB near
maximum brightness. The amplitude and the position angle of the `transient
polarization' were almost constant with wavelength in both two events. There
was a difference by about 20 degrees in the position angle between the two
events. Each event could be explained by light scattering due to short-lived
dust puff occasionally ejected off the line of sight. The flatness of the
polarization against the wavelength suggests that the scatterer is a mixture of
dust grains having various sizes. The rapid growth and fading of the transient
polarization favors the phenomenological model of dust formation near the
stellar photosphere (e.g., within two stellar radii) proposed for the time
evolution of brightness and chromospheric emission lines during deeply
declining periods, although the fading timescale can hardly be explained by a
simple dispersal of expanding dust puff with a velocity of km s
. Higher expansion velocity or some mechanism to destroy the dust grains
should be needed.Comment: 22 pages, 10 figures, accepted for publication in A
Direct imaging of a massive dust cloud around R Coronae Borealis
We present recent polarimetric images of the highly variable star R CrB using
ExPo and archival WFPC2 images from the HST. We observed R CrB during its
current dramatic minimum where it decreased more than 9 mag due to the
formation of an obscuring dust cloud. Since the dust cloud is only in the
line-of-sight, it mimics a coronograph allowing the imaging of the star's
circumstellar environment. Our polarimetric observations surprisingly show
another scattering dust cloud at approximately 1.3" or 2000 AU from the star.
We find that to obtain a decrease in the stellar light of 9 mag and with 30% of
the light being reemitted at infrared wavelengths (from R CrB's SED) the grains
in R CrB's circumstellar environment must have a very low albedo of
approximately 0.07%. We show that the properties of the dust clouds formed
around R CrB are best fitted using a combination of two distinct populations of
grains size. The first are the extremely small 5 nm grains, formed in the low
density continuous wind, and the second population of large grains (~0.14
{\mu}m) which are found in the ejected dust clouds. The observed scattering
cloud, not only contains such large grains, but is exceptionally massive
compared to the average cloud.Comment: 8 pages, 7 figures published in A&
Remotely induced magnetism in a normal metal using a superconducting spin-valve
Superconducting spintronics has emerged in the past decade as a promising new field that seeks to open a new dimension for nanoelectronics by utilizing the internal spin structure of the superconducting Cooper pair as a new degree of freedom. Its basic building blocks are spin-triplet Cooper pairs with equally aligned spins, which are promoted by proximity of a conventional superconductor to a ferromagnetic material with inhomogeneous macroscopic magnetization. Using low-energy muon spin-rotation experiments we find an unanticipated effect, in contradiction with the existing theoretical models of superconductivity and ferromagnetism: the appearance of a magnetization in a thin layer of a non-magnetic metal (gold), separated from a ferromagnetic double layer by a 50-nm-thick superconducting layer of Nb. The effect can be controlled either by temperature or by using a magnetic field to control the state of the remote ferromagnetic elements, and may act as a basic building block for a new generation of quantum interference devices based on the spin of a Cooper pair.</p
Irreversible magnetization switching at the onset of superconductivity in a superconductor ferromagnet hybrid
We demonstrate that the magnetic state of a superconducting spin valve, that is normally controlled with an external magnetic field, can also be manipulated by varying the temperature which increases the functionality and flexibility of such structures as switching elements. In this case, switching is driven by changes in the magnetostatic energy due to spontaneous Meissner screening currents forming in the superconductor below the critical temperature. Our scanning Hall probe measurements also reveal vortex-mediated pinning of the ferromagnetic domain structure due to the pinning of quantized stray fields in the adjacent superconductor. The ability to use temperature as well as magnetic field to control the local magnetisation structure raises the prospect of potential applications in magnetic memory devices.</p
In Vivo Binding and Retention of CD4-Specific DARPin 57.2 in Macaques
The recently described Designed Ankyrin Repeat Protein (DARPin) technology can produce highly selective ligands to a variety of biological targets at a low production cost.To investigate the in vivo use of DARPins for future application to novel anti-HIV strategies, we identified potent CD4-specific DARPins that recognize rhesus CD4 and followed the fate of intravenously injected CD4-specific DARPin 57.2 in rhesus macaques. The human CD4-specific DARPin 57.2 bound macaque CD4(+) cells and exhibited potent inhibitory activity against SIV infection in vitro. DARPin 57.2 or the control E3_5 DARPin was injected into rhesus macaques and the fate of cell-free and cell-bound CD4-specific DARPin was evaluated. DARPin-bound CD4(+) cells were detected in the peripheral blood as early as 30 minutes after the injection, decreasing within 6 hours and being almost undetectable within 24 hours. The amount of DARPin bound was dependent on the amount of DARPin injected. CD4-specific DARPin was also detected on CD4(+) cells in the lymph nodes within 30 minutes, which persisted with similar kinetics to blood. More extensive analysis using blood revealed that DARPin 57.2 bound to all CD4(+) cell types (T cells, monocytes, dendritic cells) in vivo and in vitro with the amount of binding directly proportional to the amount of CD4 on the cell surface. Cell-free DARPins were also detected in the plasma, but were rapidly cleared from circulation.We demonstrated that the CD4-specific DARPin can rapidly and selectively bind its target cells in vivo, warranting further studies on possible clinical use of the DARPin technology
The fall and rise of V854 Centauri: long-term ultraviolet spectroscopy of a highly-active R Coronae Borealis star
We examine long-term low-dispersion IUE, SWP and LWP spectroscopy of the R
Coronae Borealis (RCB) star V854 Cen, obtained across the deep 1991, 1992-1993
and 1994 declines. We also report the optical light curve for the star in the
interval 1987-1998, including multi-color photometry obtained during 1989-1998.
Analysis of the UV emission line spectra indicates most lines decay during
the deep declines on characteristic timescales comparable to that reported for
optical features. Fe, Mg and neutral C lines decay on timescales of typically
50-100 d. Other lines, notably ionized C lines, decay on longer timescales (>
200 d) or appear to be unaffected by the declines. The general nature of the UV
emission lines and other UV features during the declines is consistent with the
E1/E2/BL line-region model developed from the behavior of optical spectral
features during declines. However, the detailed line-behavior indicates large
intrinsic variability between decline events inconsistent with the simple
E1/E2/BL model. Limited temporal coverage prevents detailed examination of the
geometry of the emission line region or the obscuring dust. We also report the
first detection of the transition-region line C IV 1550 in the spectrum of an
RCB star.Comment: AJ in press (June), 7 figures, 4 table
Feasibility studies of the time-like proton electromagnetic form factor measurements with PANDA at FAIR
The possibility of measuring the proton electromagnetic form factors in the
time-like region at FAIR with the \PANDA detector is discussed. Detailed
simulations on signal efficiency for the annihilation of into a
lepton pair as well as for the most important background channels have been
performed. It is shown that precision measurements of the differential cross
section of the reaction can be obtained in a wide
angular and kinematical range. The individual determination of the moduli of
the electric and magnetic proton form factors will be possible up to a value of
momentum transfer squared of (GeV/c). The total cross section will be measured up to (GeV/c).
The results obtained from simulated events are compared to the existing data.
Sensitivity to the two photons exchange mechanism is also investigated.Comment: 12 pages, 4 tables, 8 figures Revised, added details on simulations,
4 tables, 9 figure
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