378 research outputs found
High Resolution Spectroscopy of the high galactic latitude RV Tauri star CE Virginis
Analysis of the surface composition of the suspected cool RV Tauri star CE
Vir shows no systematic trend in depletions of elements with respect to
condensation temperature. However, there is a significant depletion of the
elements with respect to the first ionization potential of the element. The
derived Li abundance of log (Li) = 1.50.2 indicates production
of Li in the star. Near infrared colours indicate sporadic dust formation close
to the photosphere.Comment: 12 pages, including 8 pages: Accepted for publication in MNRA
Constraining the parameters of globular cluster NGC 1904 from its variable star population
We present the analysis of 11 nights of V and I time-series observations of
the globular cluster NGC 1904 (M 79). Using this we searched for variable stars
in this cluster and attempted to refine the periods of known variables, making
use of a time baseline spanning almost 8 years. We use our data to derive the
metallicity and distance of NGC 1904. We used difference imaging to reduce our
data to obtain high-precision light curves of variable stars. We then estimated
the cluster parameters by performing a Fourier decomposition of the light
curves of RR Lyrae stars for which a good period estimate was possible. We also
derive an estimate for the age of the cluster by fitting theoretical isochrones
to our colour-magnitude diagram (CMD). Out of 13 stars previously classified as
variables, we confirm that 10 are bona fide variables. We cannot detect
variability in one other within the precision of our data, while there are two
which are saturated in our data frames, but we do not find sufficient evidence
in the literature to confirm their variability. We also detect a new RR Lyrae
variable, giving a total number of confirmed variable stars in NGC 1904 of 11.
Using the Fourier parameters, we find a cluster metallicity [Fe/H]_ZW=-1.63 +-
0.14, or [Fe/H]_UVES=-1.57 \pm 0.18, and a distance of 13.3 +- 0.4 kpc (using
RR0 variables) or 12.9 kpc (using the one RR1 variable in our sample for which
Fourier decomposition was possible).Comment: 14 pages, 11 figures, accepted for publication in A&
A Theoretical Study on Spin-Dependent Transport of "Ferromagnet/Carbon Nanotube Encapsulating Magnetic Atoms/Ferromagnet" Junctions with 4-Valued Conductances
As a novel function of ferromagnet (FM)/spacer/FM junctions, we theoretically
investigate multiple-valued (or multi-level) cell property, which is in
principle realized by sensing conductances of four states recorded with
magnetization configurations of two FMs; (up,up), (up,down), (down,up),
(down,down). In order to sense all the states, 4-valued conductances
corresponding to the respective states are necessary. We previously proposed
that 4-valued conductances are obtained in FM1/spin-polarized spacer (SPS)/FM2
junctions, where FM1 and FM2 have different spin polarizations, and the spacer
depends on spin [J. Phys.: Condens. Matter 15, 8797 (2003)]. In this paper, an
ideal SPS is considered as a single-wall armchair carbon nanotube encapsulating
magnetic atoms, where the nanotube shows on-resonance or off-resonance at the
Fermi level according to its length. The magnitude of the obtained 4-valued
conductances has an opposite order between the on-resonant nanotube and the
off-resonant one, and this property can be understood by considering electronic
states of the nanotube. Also, the magnetoresistance ratio between (up,up) and
(down,down) can be larger than the conventional one between parallel and
anti-parallel configurations.Comment: 10 pages, 4 figures, accepted for publication in J. Phys.: Condens.
Matte
Dyeing of cotton yarn with marigold (Tagetes erecta) petals: An emphasis on pre-treatments and mordants
Natural dyes and eco-friendly finishing of textile fabrics is gaining popularity because of the consciousness of people in saving the ecology. Widely available resources in India have encouraged researchers in experimenting on extraction and application of dyes for textile colouration. The aim of the present experiment was to standardize a protocol for optimization of pre-treatment, mordanting and dyeing of cotton yarn with African marigold flower petals. Myrobolan, pomegranate rind and tamarind hull were utilized in different concentrations for pre-treatment. Effect of different mordants and pre-treatment concentrations on colour strength (K/S, L, a* and b*) parameters of the cotton yarn is was studied. Optimised pre-treatment concentrations, mordants and dyeing techniques on colour fastness parameters are also presented. Myrobolan followed by pomegranate rind pre-treatment produced darker and even shades on cotton yarns. Metallic salts viz., Stannous Chloride, Copper Sulphate and Ferrous Sulphate proved to produce shades with good to excellent colour fastness properties
Synthesis, structure and ionic conductivity in scheelite type Li<sub>0.5</sub>Ce<sub>0.5-x</sub>Ln<sub>x</sub>MoO<sub>4</sub> (x = 0 and 0.25, Ln = Pr, Sm)
Scheelite type solid electrolytes, Li0.5Ce0.5-xLnxMoO4 (x = 0 and 0.25, Ln = Pr, Sm) have been synthesized using a solid state method. Their structure and ionic conductivity (σ) were obtained by single crystal X-ray diffraction and ac-impedance spectroscopy, respectively. X-ray diffraction studies reveal a space group of I41/a for Li0.5Ce0.5-xLnxMoO4 (x = 0 and 0.25, Ln = Pr, Sm) scheelite compounds. The unsubstituted Li0.5Ce0.5-xLnxMoO4 showed lithium ion conductivity ∼10−5-10−3 Ω−1cm−1 in the temperature range of 300-700°C (σ = 2.5 × 10−3 Ω−1cm−1 at 700°C). The substituted compounds show lower conductivity compared to the unsubstituted compound, with the magnitude of ionic conductivity being two (in the high temperature regime) to one order (in the low temperature regime) lower than the unsubstituted compound. Since these scheelite type structures show significant conductivity, the series of compounds could serve in high temperature lithium battery operations
A charge density study of an intramolecular charge-transfer quinoid compound with strong NLO properties
An experimental charge density investigation of 7,7-di[(S)-(+)-2-(methoxymethyl)pyrrolidino]-8,8-dicyanoquinodimethane establishes the presence of a large charge separation as well as a high in-crystal dipole moment compared to the free molecule in frozen geometry, consistent with the high SHG activity of the compound
Metal nanoparticles and their assemblies
Metal nanoparticles of varying sizes can be prepared by physical as well as chemical methods. They exhibit many fascinating properties, the size-dependent metal to nonmetal transition being an important one. Metal nanoparticles capped by thiols can be organized into ordered one-, two- and three-dimensional structures and these structures have potential applications in nanodevices. In this context, organization of arrays of metal nanoparticles with a fixed number of atoms assumes significance
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