4,377 research outputs found
Effects of tidally enhanced stellar wind on the horizontal branch morphology of globular clusters
Metallicity is the first parameter to influence the horizontal branch (HB)
morphology of globular clusters (GCs). It has been found, however, that some
other parameters may also play an important role in affecting the morphology.
While the nature of these important parameters remains unclear, they are
believed to be likely correlated with wind mass-loss of red giants, since this
mass loss determines their subsequent locations on the HB. Unfortunately, the
mass loss during the red giant stages of the stellar evolution is poorly
understood at present. The stellar winds of red giants may be tidally enhanced
by companion stars if they are in binary systems. We investigate evolutionary
consequences of red giants in binaries by including tidally enhanced stellar
winds, and examine the effects on the HB morphology of GCs. We find that red,
blue, and extreme horizontal branch stars are all produced under the effects of
tidally enhanced stellar wind without any additional assumptions on the
mass-loss dispersion. Furthermore, the horizontal branch morphology is found to
be insensitive to the tidal enhancement parameter, Bw. We compare our
theoretical results with the observed horizontal branch morphology of globular
cluster NGC 2808, and find that the basic morphology of the horizontal branch
can be well reproduced. The number of blue horizontal branch stars in our
calculations, however, is lower than that of NGC 2808.Comment: 7 pages, 4 figures, 2 tables, accepted for publication in Astronomy &
Astrophysic
Parity-time electromagnetic diodes in a two-dimensional nonreciprocal photonic crystal
We propose a kind of electromagnetic (EM) diode based on a two-dimensional nonreciprocal gyrotropic photonic crystal. This
periodic microstructure has separately broken symmetries in both parity
(P) and time-reversal (T) but obeys parity-time (PT) symmetry. This
kind of diode could support bulk one-way propagating modes either for
group velocity or phase velocity with various types of negative and
positive refraction. This symmetry-broken system could be a platform to
realize abnormal photoelectronic devices, and it may be analogous to an
electron counterpart with one-way features
Supercapacitor Performance of Nickel-Cobalt Sulfide Nanotubes Decorated Using Ni Co-Layered Double Hydroxide Nanosheets Grown in Situ on Ni Foam
In this study, to fabricate a non-binder electrode, we grew nickel-cobalt sulfide (NCS) nanotubes (NTs) on a Ni foam substrate using a hydrothermal method through a two-step approach, namely in situ growth and an anion-exchange reaction. This was followed by the electrodeposition of double-layered nickel-cobalt hydroxide (NCOH) over a nanotube-coated substrate to fabricate NCOH core-shell nanotubes. The final product is called NCS@NCOH herein. Structural and morphological analyses of the synthesized electrode materials were conducted via SEM and XRD. Different electrodeposition times were selected, including 10, 20, 40, and 80 s. The results indicate that the NCSNTs electrodeposited with NCOH nanosheets for 40 s have the highest specific capacitance (SC), cycling stability (2105 Fg-1 at a current density of 2 Ag-1), and capacitance retention (65.1% after 3,000 cycles), in comparison with those electrodeposited for 10, 20, and 80 s. Furthermore, for practical applications, a device with negative and positive electrodes made of active carbon and NCS@NCOH was fabricated, achieving a high-energy density of 23.73 Whkg-1 at a power density of 400 Wkg-1
Theoretical Study on Rotational Bands and Shape Coexistence of {Tl} in the Particle Triaxial-Rotor Model
By taking the particle triaxial-rotor model with variable moment of inertia,
we investigate the energy spectra, the deformations and the single particle
configurations of the nuclei Tl systemically. The calculated
energy spectra agree with experimental data quite well. The obtained results
indicate that the aligned bands observed in Tl originate from
the , , proton
configuration coupled to a prolate deformed core, respectively. Whereas, the
negative parity bands built upon the isomeric states in
Tl are formed by a proton with the
configuration coupled to a core with triaxial oblate deformation, and the
positive parity band on the isomeric state in Tl is
generated by a proton with configuration coupled to a
triaxial oblate core.Comment: 16 pages, 5 figures. To appear in Physical Review
Role of graphene on hierarchical flower-like NiAl layered double hydroxide-nickel foam-graphene as binder-free electrode for high-rate hybrid supercapacitor
In this work, a facile two-step hydrothermal method was reported to grow hierarchical flower-like NiAl layered double hydroxide (LDH) directly on 3D nickel foam (NF) which was further coated with 2D graphene nanosheets (GNS) layers as binder-free supercapacitor electrode. The positive and negative effects of GNS on the electrochemical performance of LDH-NF electrode were investigated in detail. The prepared LDH-NF/GNS electrode maintained an enhanced specific capacity of 165.6 C g-1 after 4000 cycles at a high current density of 40 A g-1. Furthermore, a hybrid supercapacitor, with LDH-NF/GNS and GNS-NF as the positive and negative electrodes, achieved an energy density (31.5 Wh kg-1 at a power density of 400 W kg-1) and super long-term cycle stability (a specific capacity of 67.2 C g-1 at 5 A g-1 after 5000 cycles with 80% retention). This study not only opens up the possibility of engineering LDH-NF/GNS into a promising electrode, but also highlights the positive and negative roles of GNS on LDH-NF as binder-free electrodes for further development of high-performance supercapacitors
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