23 research outputs found
Optical Multicolor WBVR-Observations of the X-Ray Star V1341 Cyg = Cyg X-2 in 1986-1992
We present the results of observations of the low-mass X-ray binary
V1341 X--2. Our observations include a total of
2375 individual measurements in four bands on 478 nights in 1986-1992. We tied
the comparison and check stars used for the binary to the catalog using
their magnitudes. The uncertainty of this procedure was 3 in the
and bands and 8%-10% for the and bands. In quiescence, the
amplitude of the periodic component in the binary's brightness variations
is within ( in ); this is due
to the ellipsoidal shape of the optical component, which is distorted with
gravitational forces from the X-ray component. Some of the system's active
states (long flares) may be due to instabilities in the accretion disk, and
possibly to instabilities of gas flows and other accretion structures. The
binary possesses a low-luminosity accretion disk. The light curves reveal no
indications of an eclipse near the phases of the upper and lower conjunctions
in quiescence or in active states during the observed intervals. We conclude
that the optical star in the close binary V1341
X-2 is a red giant rather than a blue straggler. We studied the long-term
variability of the binary during the seven years covered by our observations.
The optical observations presented in this study are compared to X-ray data
from the Ginga observatory for the same time intervals.Comment: 35 pages, 8 figure
Flexible highly conductive films based on expanded graphite /polymer nanocomposites
Highly electrically and thermally conducting films of expanded graphite/polymer nanocomposites were fabricated using an approach based on solution mixing methods. The use of Hydroxyethylcellulose and benzylic alcohol based solutions provides efficient dispersion and better exfoliation of multilayer graphene (nanographite) flakes that are further aligned in extended 2D layers forming continuous conductive pathways during lamination (hot calendering) process. Very high electrical conductivity (190 S/cm) was obtained for fabricated layered films. In contrast, for films produced by a conventional mixing and deposition method with acrylic copolymer and the same nanographitic material, with flakes randomly distributed within the composite, much lower conductivities (2.4 S/cm) were obtained
On the Construction of a New 3D Atlas of Stellar Spectral Energy Distributions
Modern spectrophotometric atlases are burdened with significant systematic errors. In particular, the problems of spectrum calibration in the ultraviolet region are not solved; different parts of the spectrum are not thoroughly fit to each other; spectra of (even bright) stars, obtained by different authors, display large discrepancies. Here we discuss a possibility to construct a new atlas of spectral energy distributions (SEDs) for a large set of stars by comparison of empirical stellar spectra in dozens of modern spectrophotometric atlases, as well as the comparison of synthetic and observed color indices in different multicolor photometric systems. In this way we suppose to exclude most of systematic errors and construct a new three-dimensional (spectral class, luminosity class, metallicity) atlas of empirical stellar spectra for several thousand stars. After exclusion of interstellar reddenings, a semi-empirical atlas of average SEDs can be constructed for about 150–200 spectral subtypes. This would allow us to make calibrations of spectrophotometric and photometric parameters in terms of spectral types and physical parameters (Teff, log g, [m/H]) and to verify the accuracy of model stellar atmospheres
Raman spectra of multilayer graphene under high temperatures
FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIGFor graphitic materials, Raman technique is a common method for temperature measurements through analysis of phonon frequencies. Temperature (T) induced downshift of the bond-stretching G mode (Delta G) is well known, but experimentally obtained thermal c3238110FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIGFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIG2018/21623-0Sem informaçãoSem informaçãoThis work has been supported by São Paulo Research Foundation (FAPESP), process No. 2018/21623-0; National Council for Scientific and Technological Development (CNPq); Russian Foundation for Basic Research (RFFI), Grant No. 18-29-19137_mk. A V A, R S, S
Three‐dimensional Parameterization of the Stellar Locus with Application to QSO Color Selection
Ripplocation in graphite nanoplatelets during sonication assisted liquid phase exfoliation
CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSDefects induced by liquid-phase exfoliation of graphite using sonication were studied. It was shown that localized impact by cavitation shock waves can produce bulk ripplocations and various types of dislocations in graphite nanoplatelets. Formation of ripples is more pronounced in large aspect (length/width) ratio platelets or nanobelts. Quasi-periodical ripple systems were observed in many nanobelts after sonication. Mechanism of formation of ripples and dislocations during sonication was proposed. Surprisingly, fast high-temperature processing was found to anneal most of defects. This is consistent with our observations that defects associated with ripplocations are strongly localized and thus can be fast annealed.129826829CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFINEP - FINANCIADORA DE ESTUDOS E PROJETOSAgências de fomento estrangeiras apoiaram essa pesquisa, mais informações acesse artig
Gas Sensors Based on Locally Heated Multiwall Carbon Nanotubes Decorated with Metal Nanoparticles
We report the design and fabrication of microreactors and sensors based on metal nanoparticle-decorated carbon nanotubes. Titanium adhesion layers and gold films were sputtered onto Si/SiO2 substrates for obtaining the electrical contacts. The gold layers were electrochemically thickened until 1 μm and the electrodes were patterned using photolithography and wet chemical etching. Before the dielectrophoretic deposition of the nanotubes, a gap 1 μm wide and 5 μm deep was milled in the middle of the metallic line by focused ion beam, allowing the fabrication of sensors based on suspended nanotubes bridging the electrodes. Subsequently, the sputtering technique was used for decorating the nanotubes with metallic nanoparticles. In order to test the as-obtained sensors, microreactors (100 μL volume) were machined from a single Kovar piece, being equipped with electrical connections and 1/4′′ Swagelok-compatible gas inlet and outlets for controlling the atmosphere in the testing chamber. The sensors, electrically connected to the contact pins by wire-bonding, were tested in the 10−5 to 10−2 W working power interval using oxygen as target gas. The small chamber volume allowed the measurement of fast characteristic times (response/recovery), with the sensors showing good sensitivity