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Polyisoprene Captured Sulfur Nanocomposite Materials for High-Areal-Capacity Lithium Sulfur Battery
A polyisoprene-sulfur (PIPS) copolymer and nano sulfur composite material (90 wt % sulfur) is synthesized through inverse vulcanization of PIP polymer with micrometer-sized sulfur particles for high-areal-capacity lithium sulfur batteries. The polycrystalline structure and nanodomain nature of the copolymer are revealed through high-resolution transmission electron microscopy (HRTEM). PIP polymer is also used as binders for the electrode to further capture the dissovlved polysulfides. A high areal capacity of ca. 7.0 mAh/cm2 and stable cycling are achieved based on the PIPS nanosulfur composite with a PIP binder, crucial to commercialization of lithium sulfur batteries. The chemical confinement both at material and electrode level alleviates the diffusion of polysulfides and the shuttle effect. The sulfur electrodes, both fresh and cycled, are analyzed through scanning electron microscopy (SEM). This approach enables scalable material production and high sulfur utilization at the cell level
Sectoral r modes and periodic RV variations of Sun-like stars
Radial velocity (RV) measurements are used to search for planets orbiting
late-type main-sequence stars and confirm the transiting planets. The most
advanced spectrometers are approaching a precision of cm/s that
implies the need to identify and correct for all possible sources of RV
oscillations intrinsic to the star down to this level and possibly beyond. The
recent discovery of global-scale equatorial Rossby waves in the Sun, also
called r modes, prompted us to investigate their possible signature in stellar
RV measurements. R modes are toroidal modes of oscillation whose restoring
force is the Coriolis force and propagate in the retrograde direction in a
frame that corotates with the star. The solar r modes with azimuthal orders were identified unambiguously because of their dispersion
relation and their long e-folding lifetimes of hundreds of days. Here we
simulate the RV oscillations produced by sectoral r modes with assuming a stellar rotation period of 25.54 days and a maximum amplitude of
the surface velocity of each mode of 2 m/s. This amplitude is representative of
the solar measurements, except for the mode which has not yet been
observed. Sectoral r modes with azimuthal orders and would produce RV
oscillations with amplitudes of 76.4 and 19.6 cm/s and periods of 19.16 and
10.22 days, respectively, for a star with an inclination of the rotation axis
. Therefore, they may produce rather sharp peaks in the Fourier
spectrum of the radial velocity time series that could lead to spurious
planetary detections. Sectoral r~modes may represent a source of confusion in
the case of slowly rotating inactive stars that are preferential targets for RV
planet search. The main limitation of the present investigation is the lack of
observational constraint on the amplitude of the mode on the Sun.Comment: 7 pages; 4 figures; 1 table; accepted to Astronomy & Astrophysic
Validating foundry technologies for extended mission profiles
This paper presents a process qualification and characterization strategy that can extend the foundry process reliability potential to meet specific automotive mission profile requirements. In this case study, data and analyses are provided that lead to sufficient confidence for pushing the allowed mission profile envelope of a process towards more aggressive (automotive) applications.\ud
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A new class of -d topological superconductor with topological classification
The classification of topological states of matter depends on spatial
dimension and symmetry class. For non-interacting topological insulators and
superconductors the topological classification is obtained systematically and
nontrivial topological insulators are classified by either integer or .
The classification of interacting topological states of matter is much more
complicated and only special cases are understood. In this paper we study a new
class of topological superconductors in dimensions which has
time-reversal symmetry and a spin conservation symmetry. We
demonstrate that the superconductors in this class is classified by
when electron interaction is considered, while the
classification is without interaction.Comment: 5 pages main text and 3 pages appendix. 1 figur
Development of ultra-high performance concrete with high fire resistance
© 2018 Elsevier Ltd Fire or high temperature is a big challenge to ultra-high performance concrete (UHPC). Strength loss of UHPCs can reach up to 80% after exposure to 800 °C. In this study, a total of six UHPC mixtures were designed and tested after subjected to elevated temperatures up to 1000 °C. The effects of aggregate type, fibre type and heating rate were investigated. Residual compressive strengths and stress-strain relationships were studied. Besides, attention was paid to explosive spalling since UHPCs are usually of compact structure and thus more vulnerable to explosive spalling than other concretes. Scanning electron microscope (SEM) analysis was conducted to help understand the mechanism of variation of internal structure under different temperatures. It was found the mixture containing steel slag and hybrid fibre had excellent fire resistance. After being subjected to 1000 °C, this mixture retained a residual compressive strength of 112.8 MPa or a relative value of 69%
Central mode and spin confinement near the boundary of the superconducting phase in YBa2Cu3O6.353 (Tc=18 K)
We have mapped the neutron scattering spin spectrum at low-energies in
YBa2Cu3O6.353 (Tc=18 K) where the doping ~0.06 is near the critical value
(pc=0.055) for superconductivity. No coexistence with long range ordered
antiferromagnetism is found. The spins fluctuate on two energy scales, one a
damped spin response with a ~2 meV relaxation rate and the other a central mode
with a relaxation rate that slows to less than 0.08 meV below Tc. The spectrum
mirrors that of a soft mode driving a central mode. Extremely short correlation
lengths, 42+-5 Angstrom in-plane and 8+-2 Angstrom along the c direction, and
isotropic spin orientations for the central mode indicate that the correlations
are subcritical with respect to any second order transition to Neel order. The
dynamics follows a model where damped spin fluctuations are coupled to the slow
fluctuations of regions with correlations shortened by the hole doping.Comment: 5 pages 4 figures. One figure revised and some text revision.
Accepted PRB Rapids February 14, 200
Magnetization reversal in Kagome artificial spin ice studied by first-order reversal curves
Magnetization reversal of interconnected Kagome artificial spin ice was
studied by the first-order reversal curve (FORC) technique based on the
magneto-optical Kerr effect and magnetoresistance measurements. The
magnetization reversal exhibits a distinct six-fold symmetry with the external
field orientation. When the field is parallel to one of the nano-bar branches,
the domain nucleation/propagation and annihilation processes sensitively depend
on the field cycling history and the maximum field applied. When the field is
nearly perpendicular to one of the branches, the FORC measurement reveals the
magnetic interaction between the Dirac strings and orthogonal branches during
the magnetization reversal process. Our results demonstrate that the FORC
approach provides a comprehensive framework for understanding the magnetic
interaction in the magnetization reversal processes of spin-frustrated systems
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