14,859 research outputs found
Thermal activation energy of 3D vortex matter in NaFe1-xCoxAs (x=0.01, 0.03 and 0.07) single crystals
We report on the thermally activated flux flow dependency on the doping
dependent mixed state in NaFe1-xCoxAs (x=0.01, 0.03, and 0.07) crystals using
the magnetoresistivity in the case of B//c-axis and B//ab-plane. It was found
clearly that irrespective of the doping ratio, magnetoresistivity showed a
distinct tail just above the Tc, offset associated with the thermally activated
flux flow (TAFF) in our crystals. Furthermore, in TAFF region the temperature
dependence of the activation energy follows the relation U(T, B)=U_0 (B)
(1-T/T_c )^q with q=1.5 in all studied crystals. The magnetic field dependence
of the activation energy follows a power law of U_0 (B)~B^(-{\alpha}) where the
exponent {\alpha} is changed from a low value to a high value at a crossover
field of B=~2T, indicating the transition from collective to plastic pinning in
the crystals. Finally, it is suggested that the 3D vortex phase is the dominant
phase in the low-temperature region as compared to the TAFF region in our
series samples
The Dropping of In-Medium Hadron Mass in Holographic QCD
We study the baryon density dependence of the vector meson spectrum using the
D4/D6 system together with the compact D4 baryon vertex. We find that the
vector meson mass decreases almost linearly in density at low density for small
quark mass, but saturates to a finite non-zero value for large density. We also
compute the density dependence of the mass and the
velocity. We find that in medium, our model is consistent with the GMOR
relation up to a few times the normal nuclear density. We compare our hQCD
predictions with predictions made based on hidden local gauge theory that is
constructed to model QCD.Comment: 20 pages, 7 figure
Epitaxial growth and the magnetic properties of orthorhombic YTiO3 thin films
High-quality YTiO3 thin films were grown on LaAlO3 (110) substrates at low
oxygen pressures (<10-8 Torr) using pulsed laser deposition. The in-plane
asymmetric atomic arrangements at the substrate surface allowed us to grow
epitaxial YTiO3 thin films, which have an orthorhombic crystal structure with
quite different a- and b-axes lattice constants. The YTiO3 film exhibited a
clear ferromagnetic transition at 30 K with a saturation magnetization of about
0.7 uB/Ti. The magnetic easy axis was found to be along the [1-10] direction of
the substrate, which differs from the single crystal easy axis direction, i.e.,
[001].Comment: 14 pages, 4 figure
Extensive spatiotemporal analyses of surface ozone and related meteorological variables in South Korea for the period 1999–2010
Spatiotemporal characteristics of surface ozone (O<sub>3</sub>) variations over
South Korea are investigated with consideration of meteorological factors
and timescales based on the Kolmogorov–Zurbenko filter (KZ filter), using
measurement data at 124 air quality monitoring sites and 72 weather stations
for the 12 yr period of 1999–2010. In general, O<sub>3</sub> levels at coastal
cities are high due to dynamic effects of the sea breeze while those at the
inland and Seoul Metropolitan Area (SMA) cities are low due to the NO<sub>x</sub>
titration by local precursor emissions. We examine the meteorological
influences on O<sub>3</sub> using a combined analysis of the KZ filter and linear
regressions between O<sub>3</sub> and meteorological variables. We decomposed
O<sub>3</sub> time series at each site into short-term, seasonal, and long-term
components by the KZ filter and regressed on meteorological variables.
Impact of temperature on the O<sub>3</sub> levels is significantly high in the
highly populated SMA and inland region, but low in the coastal region. In
particular, the probability of high O<sub>3</sub> occurrence doubles with
4 °C of temperature increase in the SMA during high O<sub>3</sub> months
(May–October). This implies that those regions will experience frequent
high O<sub>3</sub> events in a future warming climate. In terms of short-term
variation, the distribution of high O<sub>3</sub> probability classified by wind
direction shows the effect of both local precursor emissions and long-range
transport from China. In terms of long-term variation, the O<sub>3</sub>
concentrations have increased by +0.26 ppbv yr<sup>−1</sup> (parts per billion by volume) on nationwide
average, but their trends show large spatial variability. Singular value
decomposition analyses further reveal that the long-term temporal evolution
of O<sub>3</sub> is similar to that of nitrogen dioxide, although the spatial
distribution of their trends is different. This study will be helpful as a
reference for diagnostics and evaluation of regional- and local-scale
O<sub>3</sub> and climate simulations, and as a guide to appropriate O<sub>3</sub>
control policy in South Korea
Effects of pressure on the ferromagnetic state of the CDW compound SmNiC2
We report the pressure response of charge-density-wave (CDW) and
ferromagnetic (FM) phases of the rare-earth intermetallic SmNiC2 up to 5.5 GPa.
The CDW transition temperature (T_{CDW}), which is reflected as a sharp
inflection in the electrical resistivity, is almost independent of pressure up
to 2.18 GPa but is strongly enhanced at higher pressures, increasing from 155.7
K at 2.2 GPa to 279.3 K at 5.5 GPa. Commensurate with the sharp increase in
T_{CDW}, the first-order FM phase transition, which decreases with applied
pressure, bifurcates into the upper (T_{M1}) and lower (T_c) phase transitions
and the lower transition changes its nature to second order above 2.18 GPa.
Enhancement both in the residual resistivity and the Fermi-liquid T^2
coefficient A near 3.8 GPa suggests abundant magnetic quantum fluctuations that
arise from the possible presence of a FM quantum critical point.Comment: 5 pages, 5 figure
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