1,735 research outputs found
Metal-nonmetal transition in LixCoO2 thin film and thermopower enhancement at high Li concentration
We investigate the transport properties of LixCoO2 thin films whose
resistivities are nearly an order of magnitude lower than those of the bulk
polycrystals. A metal-nonmetal transition occurs at ~0.8 in a biphasic domain,
and the Seebeck coefficient (S) is drastically increased at ~140 K (= T*) with
increasing the Li concentration to show a peak of magnitude ~120 \muV/K in the
S-T curve of x = 0.87. We show that T* corresponds to a crossover temperature
in the conduction, most likely reflecting the correlation-induced temperature
dependence in the low-energy excitations
Pruning Algorithms for Pretropisms of Newton Polytopes
Pretropisms are candidates for the leading exponents of Puiseux series that
represent solutions of polynomial systems. To find pretropisms, we propose an
exact gift wrapping algorithm to prune the tree of edges of a tuple of Newton
polytopes. We prefer exact arithmetic not only because of the exact input and
the degrees of the output, but because of the often unpredictable growth of the
coordinates in the face normals, even for polytopes in generic position. We
provide experimental results with our preliminary implementation in Sage that
compare favorably with the pruning method that relies only on cone
intersections.Comment: exact, gift wrapping, Newton polytope, pretropism, tree pruning,
accepted for presentation at Computer Algebra in Scientific Computing, CASC
201
Composition of primary cosmic rays at energies 10(15) to approximately 10(16) eV
The sigma epsilon gamma spectrum in 1 approx. 5 x 1000 TV observed at Mt. Fuji suggests that the flux of primary protons 10 to the 15 approx 10th eV is lower by a factor of 2 approx. 3 than a simple extrapolation from lower energies; the integral proton spectrum tends to be steeper than around to the power V and the spectral index tends to be steeper than Epsilon to the -17th power around 10 to the 14th power eV and the spectral index becomes approx. 2.0 around 10 to the 15th power eV. If the total flux of primary particles has no steepening up to approx 10 to the 15th power eV, than the fraction of primary protons to the total flux should be approx 20% in contrast to approx 45% at lower energies
EXPERIMENTAL AND NUMERICAL STUDIES ON LOCAL HIGH EFFICIENCY AIR CONDITIONING SYSTEM FOR OFFICE BUILDINGS
ABSTRACT The effects of an air conditioning system for office buildings were studied experimentally and computationally. A displacement ventilation system was used as the main air-conditioning system, and a partition with a built-in circular fan was used to deliver the air-conditioned clean air near the floor supplied by the main displacement system to the occupant in the office directly. Experimental model tests and computational analysis that used the large eddy simulation (LES) have been carried out to obtain local air exchange efficiency, air temperature and air velocity distributions in a test chamber. The measured and simulated air velocities were compared. The results show that the partition's built-in circular fan has a great impact on the local air exchange efficiency in the immediate vicinity of the occupant. However, the thermal comfort of the occupant should be examined in more thoroughly
Band-Gap Nonlinearity in Lead Chalcogenide (PbQ, Q = Te, Se, S) Alloys
Narrow band-gap lead chalcogenides have been developed
for several optical and electronic applications. However, band-gap energies
of the ternary and quaternary alloys have received little attention compared
with the parent binary phases. Here, we have fabricated single-phase
ternary (PbTe)1−x(PbSe)x and quaternary (PbTe)0.9−y(PbSe)0.1(PbS)y and
(PbTe)0.65−z(PbSe)0.35(PbS)z alloys and shown that although lattice
parameters follow Vegard’s law as a function of composition, the bandgap
energies exhibit a substantial bowing effect. The ternary
(PbTe)1−x(PbSe)x system features a smaller bowing parameter predominantly
due to the difference in electronegativity between Se and Te,
whereas the larger bowing parameters in quaternary alloys are generated
from a larger crystal lattice mismatch and larger miscibility gap. These
findings can lead to further advances in tuning the band-gap and lattice
parameters for optical and electronic applications of lead chalcogenides
On the possible generation of the young massive open clusters Stephenson2 and BDSB122 by Omega Centauri
A massive objects such as a globular cluster passing through the disk of a
galaxy can trigger star formation. We test the hypothesis that the most massive
globular cluster in the Galaxy, Centauri, which crossed the disk
approximately Myr ago, may have triggered the formation of the open
clusters Stephenson 2 and BDSB 122. The orbits of Centauri, Stephenson
2 and BDSB 122 are computed for the three-component model of Johnston,
Hernquist & Bolte, which considers the disk, spheroidal and halo gravitational
potentials. With the re-constructed orbit of Centauri, we show that
the latest impact site is consistent, within important uncertainties, with the
birth-site of the young massive open clusters BDSB 122 and Stephenson 2. Within
uncertainties, this scenario is consistent with the time-scale of their
backwards motion in the disk, shock wave propagation and delay for star
formation. Together with open cluster formation associated to density waves in
spiral arms, the present results are consistent with the idea that massive
globular clusters as additional progenitors of open clusters, the massive ones
in particular.Comment: 6 pages, 4 figures; accepted by A&
The s-wave charmed baryon resonances from a coupled-channel approach with heavy quark symmetry
We study charmed baryon resonances which are generated dynamically within a
unitary meson-baryon coupled channel model that treats the heavy pseudoscalar
and vector mesons on equal footing as required by heavy-quark symmetry. It is
an extension of recent SU(4) models with t-channel vector meson exchanges to a
SU(8) spin-flavor scheme, but differs considerably from the SU(4) approach in
how the strong breaking of the flavor symmetry is implemented. Some of our
dynamically generated states can be readily assigned to recently observed
baryon resonances, while others do not have a straightforward identification
and require the compilation of more data as well as an extension of the model
to d-wave meson-baryon interactions and p-wave coupling in the neglected s- and
u-channel diagrams. Of several novelties, we find that the Lambda_c(2595),
which emerged as a ND quasi-bound state within the SU(4) approaches, becomes
predominantly a ND* quasi-bound state in the present SU(8) scheme.Comment: 37 pages, 7 figures. Some parameters of the model have been changed,
more channels are considered. To appear in PR
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