195 research outputs found
Design and Implementation of Information Retrieval using Ontology
An approach is proposed that can be used to make these arch adaptive according to each user2019;s need using ontology .Our approach is distinct because it allows each user to perform more fine-grained search by capturing changes of each user2019;s preferences without any user effort. Such a method is not performed in typical search engines
Physical Properties of Metallic Antiferromagnetic CaCo{1.86}As2 Single Crystals
We report studies of CaCo{1.86}As2 single crystals. The electronic structure
is probed by angle-resolved photoemission spectroscopy (ARPES) measurements of
CaCo{1.86}As2 and by full-potential linearized augmented-plane-wave
calculations for the supercell Ca8Co15As16 (CaCo{1.88}As2). Our XRD crystal
structure refinement is consistent with the previous combined refinement of
x-ray and neutron powder diffraction data showing a collapsed-tetragonal
ThCr2Si2-type structure with 7(1)% vacancies on the Co sites corresponding to
the composition CaCo{1.86}As2 [D. G. Quirinale et al., Phys. Rev. B 88, 174420
(2013)]. The anisotropic magnetic susceptibility chi(T) data are consistent
with the magnetic neutron diffraction data of Quirianale et al. that
demonstrate the presence of A-type collinear antiferromagnetic order below the
Neel temperature TN = 52(1) K with the easy axis being the tetragonal c axis.
However, no clear evidence from the resistivity rho(T) and heat capacity Cp(T)
data for a magnetic transition at TN is observed. A metallic ground state is
demonstrated from band calculations and the rho(T), Cp(T) and ARPES data, and
spin-polarized calculations indicate a competition between the A-type AFM and
FM ground states. The Cp(T) data exhibit a large Sommerfield electronic
coefficient reflecting a large density of states at the Fermi energy D(EF),
consistent with the band structure calculations which also indicate a large
D(EF) arising from Co 3d bands. At 1.8 K the M(H) data for H|| c exhibit a
well-defined first-order spin-flop transition at an applied field of 3.5 T. The
small ordered moment of 0.3 muB/Co obtained from the M(H) data at low T, the
large exchange enhancement of chi and the lack of a self-consistent
interpretation of the chi(T) and M(H,T) data in terms of a local moment
Heisenberg model together indicate that the magnetism of CaCo{1.86}As2 is
itinerant.Comment: 18 pages, 15 figures, 4 tables, 61 references; v2: extended the fits
of experimental data by additional electronic structure calculations;
published versio
Characteristics of gravity waves generated in a convective and a non-convective environment revealed from hourly radiosonde observation under CPEA-II campaign
Analyses of hourly radiosonde data of temperature, wind, and relative
humidity during four days (two with convection and two with no convection)
as a part of an intensive observation period in CPEA-2 campaign over Koto
Tabang (100.32° E, 0.20° S), Indonesia, are presented.
Characteristics of gravity waves in terms of dominant wave frequencies at
different heights and their vertical wavelengths are shown in the lower
stratosphere during a convective and non-convective period. Gravity waves with
periods ~10 h and ~4–5 h were found dominant near
tropopause (a region of high stability) on all days of
observation. Vertical propagation of gravity waves were seen modified near
heights of the three identified strong wind shears (at ~16, 20, and
25 km heights) due to wave-mean flow interaction. Between 17 and 21 km
heights, meridional wind fluctuations dominated over zonal wind, whereas from
22 to 30 km heights, wave fluctuations with periods ~3–5 h and
~8–10 h in zonal wind and temperature were highly associated,
suggesting zonal orientation of wave propagation. Gravity waves from
tropopause region to 30 km heights were analyzed. In general, vertical
wavelength of 2–5 km dominated in all the mean-removed (~ weekly mean)
wind and temperature hourly profiles. Computed vertical wavelength spectra
are similar, in most of the cases, to the source spectra (1–16 km height)
except that of zonal wind spectra, which is broad during active convection.
Interestingly, during and after convection, gravity waves with short
vertical wavelength (~2 km) and short period (~2–3 h)
emerged, which were confined in the close vicinity of tropopause, and were
not identified on non-convective days, suggesting convection to be the source
for them. Some wave features near strong wind shear (at 25 km height) were
also observed with short vertical wavelengths in both convective and
non-convective days, suggesting wind shear to be the sole cause of generation
and seemingly not associated with deep convection below. A drop in the
temperature up to ~4–5 K (after removal of diurnal component) was
observed at ~16 km height near a strong wind shear (~45–55 m s<sup>−1</sup> km<sup>−1</sup>) during active period of convection
Mesoscale convection system and occurrence of extreme low tropopause temperatures: observations over Asian summer monsoon region
The present study examines the process of how tropospheric air enters the
stratosphere, particularly in association with tropical mesoscale convective
systems (TMCS) which are considered to be one of the causative mechanisms
for the observation of extremely low tropopause temperature over the
tropics. The association between the phenomena of convection and the
observation of extreme low tropopause temperature events is, therefore,
examined over the Asian monsoon region using data from multiple platforms.
Satellite observations show that the area of low outgoing long wave
radiation (OLR), which is a proxy for the enhanced convection, is embedded
with high altitude clouds top temperatures (≤193 K). A detailed
analysis of OLR and 100 hPa temperature shows that both are modulated by
westward propagating Rossby waves with a period of ~15 days,
indicating a close linkage between them. The process by which the
tropospheric air enters the stratosphere may, in turn, be determined by how
the areas of convection and low tropopause temperature (LTT) i.e. <I>T</I>≤191 K
are spatially located. In this context, the relative spatial
distribution of low OLR and LTT areas is examined. Though, the locations of
low OLR and LTT are noticed in the same broad area, the two do not always
overlap, except for partial overlap in some cases. When there are multiple
low OLR areas, the LTT area generally appears in between the low OLR areas.
Implications of these observations are also discussed. The present analysis
also shows that the horizontal mean winds have a role in the spatial
distribution of low OLR and LTT
Surface stress and lattice dynamics in oxide ultrathin films
The lattice misfit between the substrate and an epitaxial film leads in general to static forces, which define the interface stress, and dynamic responses that modify the thin-film lattice dynamics. Although these are both fundamental concepts that are important for film growth and thin-film properties, they have not been investigated in a combined way so far. Therefore, herein, surface stress experiments in combination with surface phonon studies for three different, cubic oxide ultrathin film systems are reviewed. Within the class of binary oxides, NiO(001) grown on Ag(001) is chosen, which exhibits a -2.2% lattice mismatch, and BaO(001) on Pt(001), a system with a negligible lattice mismatch. For the ternary oxides, perovskite thin films of BaTiO3 grown epitaxially on Pt(001) with a lattice mismatch of -2.3% are focused upon. The surface stress experiments are conducted with an optical two-beam curvature technique under in situ growth conditions. Surface and thin-film phonons are determined by high-resolution electron energy loss spectroscopy. Surface stress and lattice dynamics are discussed in the range from the oxide monolayer to thin films of about 20 unit cell in thickness
Exotic Kondo crossover in a wide temperature region in the topological Kondo insulator SmB6 revealed by high-resolution ARPES
Temperature dependence of the electronic structure of SmB6 is studied by
high-resolution ARPES down to 1 K. We demonstrate that there is no essential
difference for the dispersions of the surface states below and above the
resistivity saturating anomaly (~ 3.5 K). Quantitative analyses of the surface
states indicate that the quasi-particle scattering rate increases linearly as a
function of temperature and binding energy, which differs from Fermi-Liquid
behavior. Most intriguingly, we observe that the hybridization between the d
and f states builds gradually over a wide temperature region (30 K < T < 110
K). The surface states appear when the hybridization starts to develop. Our
detailed temperature-dependence results give a complete interpretation of the
exotic resistivity result of SmB6, as well as the discrepancies among
experimental results concerning the temperature regions in which the
topological surface states emerge and the Kondo gap opens, and give new
insights into the exotic Kondo crossover and its relationship with the
topological surface states in the topological Kondo insulator SmB6.Comment: 8 pages, 5 figure
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