Pressure-induced amorphization and polyamorphism in one-dimensional single crystal TiO2 nanomaterials

The structural phase transitions of single crystal TiO2-B nanoribbons were investigated in-situ at high-pressure using the synchrotron X-ray diffraction and the Raman scattering. Our results have shown a pressure-induced amorphization (PIA) occurred in TiO2-B nanoribbons upon compression, resulting in a high density amorphous (HDA) form related to the baddeleyite structure. Upon decompression, the HDA form transforms to a low density amorphous (LDA) form while the samples still maintain their pristine nanoribbon shape. HRTEM imaging reveals that the LDA phase has an {\alpha}-PbO2 structure with short range order. We propose a homogeneous nucleation mechanism to explain the pressure-induced amorphous phase transitions in the TiO2-B nanoribbons. Our study demonstrates for the first time that PIA and polyamorphism occurred in the one-dimensional (1D) TiO2 nanomaterials and provides a new method for preparing 1D amorphous nanomaterials from crystalline nanomaterials.Comment: 4 figure

Natural Resources for Therapeutic Use: Evidence from Brazil.

Identify plants used for insect stings in selfcare practices in the situation of suffering by people living in a rural location of Santa Maria municipality, Southern Brazil

The Abundance Pattern of α\alpha elements in the Triangulum-Andromeda Overdensity

The close relationship between the nature of the Triangulum-Andromeda (TriAnd) overdensity and the Galactic disk has become increasingly evident in recent years. However, the chemical pattern of this overdensity (R$_{GC}$ = 20 - 30 kpc) is unique and differs from what we know of the local disk. In this study, we analyze the chemical abundances of five $\alpha$ elements (Mg, O, Si, Ca, and Ti) in a sample of stars belonging to the TriAnd overdensity, including stars with [Fe/H] $<$ $-$1.2, to investigate the evolution of the $\alpha$ elements with metallicity. High-resolution spectra from Gemini North with GRACES were analyzed. Overall, the TriAnd population presents an $\alpha$-element pattern that differs from that of the local disk; the TriAnd stars fall in between the local disk and the dwarf galaxies in the [X/Fe] vs. [Fe/H] plane. The high [Mg/Fe] ratios obtained for the lower metallicity TriAnd stars may indicate a roughly parallel sequence to the Milky Way local disk at lower values of [Fe/H], revealing a 'knee' shifted towards lower metallicities for the TriAnd population. Similar behavior is also exhibited in the [Ca/Fe] and [Si/Fe] ratios. However, for O and Ti the behavior of the [X/Fe] ratios shows a slight decay with decreasing metallicity. Our results reinforce the TriAnd overdensity as a unique stellar population of the Milky Way, with an abundance pattern that is different from all stellar populations studied to date. The complete understanding of the complex TriAnd population will require high-resolution spectroscopic observations of a larger sample of TriAnd stars

Apparatus for processing of samples at high pressures and high temperatures in a fast quenching-rate regime and synthesis of polyacetylene by pulsed laser heating of confined carbon thin films

The pulsed laser heating of confined samples followed by ultrafast cooling constitutes an interesting route to explore the production of new phases and compounds. Indeed, in some cases the ultrafast cooling allows retaining at ambient conditions species that were produced under extreme conditions. The experimental setup described in this work allows the heating of thin film samples to temperatures ranging from 1400 to 5500 K, in a controlled and measurable way, with estimated cooling rates in excess of 1011 K s -1. In this paper, we show that the pulsed laser heating of thin amorphous carbon films deposited on copper substrates leads to the formation of polyacetylene in peak temperatures ranging from 1400 to 2600 K and static pressures between 0.8 and 1.1 GPa. The probable source of hydrogen was tracked to the small amount of water physically adsorbed at the carbon film/copper gasket interface. Because of the fast heating and cooling rate in these experiments, the hydrogen formed by water dissociation at high temperatures does not have enough time to diffuse out of the reaction cell. The results here reported strongly suggest that the evolution and stability of carbon-rich species produced by pulsed-laser heating at high pressure and high temperature critically depends on the capability of hydrogen retention in the reactional system

Triangulum–Andromeda Overdensity: a Region with a Complex Stellar Population

The Triangulum–Andromeda (TriAnd) overdensity is a distant structure of the Milky Way located in the second Galactic quadrant well below the Galactic plane. Since its discovery, its nature has been under discussion, whether it could be old perturbations of the Galactic disk or the remains of a disrupted former dwarf galaxy. In this study, we investigate the kinematics and chemical composition in 13 stars selected as TriAnd candidates from Two Micron All Sky Survey photometry. The sample was observed using the GRACES high-resolution spectrograph attached to the Gemini North telescope. Based on radial velocities obtained from the spectra and the astrometric data from Gaia, three different kinematic criteria were used to classify our sample stars as belonging to the TriAnd overdensity. The TriAnd confirmed members in our sample span a range in metallicities, including two metal-poor stars ([Fe/H] ~ −1.3 dex). We show that the adopted kinematical classification also chemically segregates TriAnd and non-TriAnd members of our sample, indicating a unique chemical pattern of the TriAnd stars. Our results indicate different chemical patterns for the [Na/Fe], [Al/Fe], [Ba/Fe], and [Eu/Fe] ratios in the TriAnd stars when compared to the chemical pattern of the local disk; the paucity of studies chemically characterizing the outer disk population of the Milky Way is the main obstacle in establishing that the TriAnd population is chemically similar to field stars in the outer disk. But the TriAnd chemical pattern is reminiscent of that found in outer disk open clusters, although the latter are significantly more metal-rich than TriAnd.FAPERJCarlos Chagas Filho Foundation for Research Support of the State of Rio de Janeiro (FAPERJ) [202.756/2016]; Brazilian Agency CAPESCAPES; FAPESPFundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2018/21250-9]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]