ABSTRACT
We announce the discovery of GPX-1 b, a transiting brown dwarf with a mass of 19.7 ± 1.6 MJup and a radius of 1.47 ± 0.10 RJup, the first substellar object discovered by the Galactic Plane ...eXoplanet (GPX) survey. The brown dwarf transits a moderately bright (V = 12.3 mag) fast-rotating F-type star with a projected rotational velocity $v\sin {\, i_*}=40\pm 10$ km s−1. We use the isochrone placement algorithm to characterize the host star, which has effective temperature 7000 ± 200 K, mass 1.68 ± 0.10 $\mathrm{\it M}_\odot$, radius 1.56 ± 0.10 $\mathrm{\it R}_\odot$, and approximate age $0.27_{-0.15}^{+0.09}$ Gyr. GPX-1 b has an orbital period of ∼1.75 d and a transit depth of 0.90 ± 0.03 per cent. We describe the GPX transit detection observations, subsequent photometric and speckle-interferometric follow-up observations, and SOPHIE spectroscopic measurements, which allowed us to establish the presence of a substellar object around the host star. GPX-1 was observed at 30-min integrations by TESS in Sector 18, but the data are affected by blending with a 3.4 mag brighter star 42 arcsec away. GPX-1 b is one of about two dozen transiting brown dwarfs known to date, with a mass close to the theoretical brown dwarf/gas giant planet mass transition boundary. Since GPX-1 is a moderately bright and fast-rotating star, it can be followed-up by the means of the Doppler tomography.
The paper discusses the possibility of manufacturing silicon nanoparticles, which are suitable for contrasting biological tissues imaged by optical coherence tomography, by femtosecond laser ablation ...of porous silicon in various liquids. The manufactured nanoparticles are characterised by average sizes of 87, 112, and 102 nm for cases of ablation in water, ethanol, and liquid nitrogen, respectively, as well as a relatively narrow size distribution, which provides additional advantages for subsequent delivery into biological tissues. Electrochemical etching, which results in the formation of layers of porous silicon, allows the yield of ablation products to be increased several-fold by lowering the ablation threshold, thereby increasing the light scattering efficiency of the prepared suspensions compared with the case of using crystalline silicon as targets. The possibility of obtaining high-contrast images of a biotissue phantom based on an agar gel with embedded nanoparticles is shown. The magnitude of the contrast depends on the liquid used for ablation and correlates with the values of the reduced scattering coefficient of the studied suspensions.
Picosecond pulsed laser ablation of meso- and microporous silicon layers in water and ethanol leads to the formation of nanosilicon suspensions with particle diameters below 100 nm. It is established ...that the use of porous silicon targets allows the laser ablation threshold to be reduced and the nanoparticle concentration increased as compared to the ablation of crystalline silicon.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Scanning electron microscopy analysis of surfaces produced via the selective laser melting technique by microsecond laser pulses of AlSi10Mg powders in vacuum and argon has been carried out. Because ...of such modification the structures are formed with micro- and nanopores with concentration depending on the geometric parameters of the particles in the starting powders, as well as on the atmosphere in which the treatment was performed. For the first time by means of the Raman spectroscopy a considerable change in the mechanical stresses and fraction of crystalline state silicon in the studied structures before and after selective laser melting was registered.
The efficiency of light scattering by nanoparticles formed using the method of picosecond laser ablation of silicon in water and by nanoparticles of mechanically grinded mesoporous silicon is ...compared. The ensembles of particles of both types possess the scattering coefficients sufficient to use them as contrast agents in optical coherence tomography (OCT), particularly in the range of wavelengths 700 – 1000 nm, where the absorption of both silicon and most biological and mimicking tissues is small. According to the Mie theory the main contribution to the scattering in this case is made by the particles having a relatively large size (150 – 300 nm). In the experiments on visualising the agar phantom surface by means of OCT, the contrast of the medium boundary, provided by nanoparticles amounted to 14 dB and 30 dB for the ablated particles and the porous silicon powder, respectively. The numerical simulation of OCT images of skin in the presence of nanoparticles, confirmed the efficiency of using them as a contrast agent.
Silicon nanoparticles with sizes of 50–300 nm have been formed via picosecond laser ablation of porous silicon and silicon microparticles in water using various targets. Raman spectroscopy has ...revealed the presence of a low amount of the amorphous phase in the obtained particles (10–12%) prepared from micro- and mesoporous silicon layers and almost a zero degree of crystallinity in the case of laser fragmentation of silicon micropowders in water. The results are promising for further application of the nanoparticles in photonics and biomedicine.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
It is demonstrated that the surface-relief orientation in the form of one-dimensional gratings with a period of 1.20 ± 0.02 μm formed under processing of hydrogenated-silicon films by femtosecond ...laser pulses (1.25 μm) with an energy density of 0.15 J/cm
2
is determined by the direction of the polarization vector of the radiation and total laser exposure. Based on the results of the analysis of Raman spectra, the presence of a nanocrystalline phase of silicon with a volume fraction between 15 and 67% (depending on processing conditions) is detected. The observed processes of micro- and nanostructuring are caused by excitation of the surface plasmon–polaritons and nanocrystallization in the near-surface region in the field of high-power femtosecond laser pulses, respectively. In addition, formation of polymorph modifications of silicon Si-III and Si-XII under femtosecond laser processing with a number of pulses exceeding 500 is discovered. Anisotropy of the Raman signal for the above polymorph modifications is revealed.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this paper, we report on the effect of buffer gas on silicon nanoparticle formation in femtosecond laser ablation process. For the first time the nonmonotonic dependence of the silicon ...nanoparticle sizes on the gas pressure is obtained. Distributions of the particles on the size received by means of atomic-force microscopy indicate reducing the Si nanoparticle diameter with pressure increase from 50 to 700 mbar for helium and nitrogen atmospheres, with the minimal nanoparticle size up to 5 nm reaching in helium. At further increase in pressure there is a growth of the nanoparticles size and distribution becomes wider. Using argon as a buffer gas results in larger nanoparticle sizes than in helium and more complicated dependence of the size distribution on the argon pressure. The electron diffraction and Raman scattering in the formed silicon nanoparticles evidence their crystallinity.
We announce the discovery of GPX-1 b, a transiting brown dwarf with a mass of \(19.7\pm 1.6\) \(M_{\mathrm{Jup}}\) and a radius of \(1.47\pm0.10\) \(R_{\mathrm{Jup}}\), the first sub-stellar object ...discovered by the Galactic Plane eXoplanet (GPX) survey. The brown dwarf transits a moderately bright (\(V\) = 12.3 mag) fast-rotating F-type star with a projected rotational velocity \(v\sin{ i_*}=40\pm10\) km/s. We use the isochrone placement algorithm to characterize the host star, which has effective temperature \(7000\pm200\) K, mass \(1.68\pm0.10\) \(M_{\mathrm{Sun}}\), radius \(1.56\pm0.10\) \(R_{\mathrm{Sun}}\) and approximate age \(0.27_{-0.15}^{+0.09}\) Gyr. GPX-1 b has an orbital period of \(\sim\)1.75 d, and a transit depth of \(0.90\pm0.03\) %. We describe the GPX transit detection observations, subsequent photometric and speckle-interferometric follow-up observations, and SOPHIE spectroscopic measurements, which allowed us to establish the presence of a sub-stellar object around the host star. GPX-1 was observed at 30-min integrations by TESS in Sector 18, but the data is affected by blending with a 3.4 mag brighter star 42 arcsec away. GPX-1 b is one of about two dozen transiting brown dwarfs known to date, with a mass close to the theoretical brown dwarf/gas giant planet mass transition boundary. Since GPX-1 is a moderately bright and fast-rotating star, it can be followed-up by the means of Doppler tomography.
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