24,610 research outputs found
Vertical variation of optical properties of mixed Asian dust/pollution plumes according to pathway of air mass transport over East Asia
© Author(s) 2015. This is an Open Access article made available under the terms of the Creative Commons Attribution License 3.0 https://creativecommons.org/licenses/by/3.0/We use five years (2009-2013) of multiwavelength Raman lidar measurements at Gwangju, South Korea (35.10° N, 126.53° E) for the identification of changes of optical properties of East Asian dust depending on its transport path over China. Profiles of backscatter and extinction coefficients, lidar ratios, and backscatter-related Ångström exponents (wavelength pair 355/532 nm) were measured at Gwangju. Linear particle depolarization ratios were used to identify East Asian dust layers. We used backward trajectory modeling to identify the pathway and the vertical position of dust-laden air masses over China during long-range transport. Most cases of Asian dust events can be described by the emission of dust in desert areas and subsequent transport over highly polluted regions of China. The Asian dust plumes could be categorized into two classes according to the height above ground at which these plumes were transported: (case I) the dust layers passed over China at high altitude levels (> 3 km) until arrival over Gwangju, and (case II) the Asian dust layers were transported near the surface and within the lower troposphere (< 3 km) over industrialized areas before they arrived over Gwangju. We find that the optical characteristics of these mixed Asian dust layers over Gwangju differ depending on their vertical position above ground over China and the change of height above ground during transport. The mean linear particle depolarization ratio was 0.21 ± 0.06 (at 532 nm), the mean lidar ratios were 52 ± 7 sr at 355 nm and 53 ± 8 sr at 532 nm, and the mean Ångström exponent was 0.74 ± 0.31 for case I. In contrast, plumes transported at lower altitudes (case II) showed low depolarization ratios (0.13 ± 0.04 at 532 nm), and higher lidar ratio (63 ± 9 sr at 355 nm and 62 ± 8 sr at 532 nm) and Ångström exponents (0.98 ± 0.51). These numbers show that the optical characteristics of mixed Asian plumes are more similar to optical characteristics of urban pollution. We find a decrease of the linear depolarization ratio of the mixed dust/pollution plume depending on transport time if the pollution layer traveled over China at low heights, i.e., below approximately 3 km above ground. In contrast, we do not find such a trend if the dust plumes traveled at heights above 3 km over China. We need a longer time series of lidar measurements in order to determine in a quantitative way the change of optical properties of dust with transport time.Peer reviewedFinal Published versio
The potential (iz)^m generates real eigenvalues only, under symmetric rapid decay conditions
We consider the eigenvalue problems -u"(z) +/- (iz)^m u(z) = lambda u(z), m
>= 3, under every rapid decay boundary condition that is symmetric with respect
to the imaginary axis in the complex z-plane. We prove that the eigenvalues
lambda are all positive real.Comment: 23 pages and 1 figur
Fermionic Superfluidity with Imbalanced Spin Populations and the Quantum Phase Transition to the Normal State
Whether it occurs in superconductors, helium-3 or inside a neutron star,
fermionic superfluidity requires pairing of fermions, particles with
half-integer spin. For an equal mixture of two states of fermions ("spin up"
and "spin down"), pairing can be complete and the entire system will become
superfluid. When the two populations of fermions are unequal, not every
particle can find a partner. Will the system nevertheless stay superfluid? Here
we study this intriguing question in an unequal mixture of strongly interacting
ultracold fermionic atoms. The superfluid region vs population imbalance is
mapped out by employing two complementary indicators: The presence or absence
of vortices in a rotating mixture, as well as the fraction of condensed fermion
pairs in the gas. Due to the strong interactions near a Feshbach resonance, the
superfluid state is remarkably stable in response to population imbalance. The
final breakdown of superfluidity marks a new quantum phase transition, the
Pauli limit of superfluidity.Comment: 15 pages, 5 figure
Neuronal glucose transporter isoform 3 deficient mice demonstrate features of autism spectrum disorders.
Neuronal glucose transporter (GLUT) isoform 3 deficiency in null heterozygous mice led to abnormal spatial learning and working memory but normal acquisition and retrieval during contextual conditioning, abnormal cognitive flexibility with intact gross motor ability, electroencephalographic seizures, perturbed social behavior with reduced vocalization and stereotypies at low frequency. This phenotypic expression is unique as it combines the neurobehavioral with the epileptiform characteristics of autism spectrum disorders. This clinical presentation occurred despite metabolic adaptations consisting of an increase in microvascular/glial GLUT1, neuronal GLUT8 and monocarboxylate transporter isoform 2 concentrations, with minimal to no change in brain glucose uptake but an increase in lactate uptake. Neuron-specific glucose deficiency has a negative impact on neurodevelopment interfering with functional competence. This is the first description of GLUT3 deficiency that forms a possible novel genetic mechanism for pervasive developmental disorders, such as the neuropsychiatric autism spectrum disorders, requiring further investigation in humans
Semiconducting-to-metallic photoconductivity crossover and temperature-dependent Drude weight in graphene
We investigated the transient photoconductivity of graphene at various
gate-tuned carrier densities by optical-pump terahertz-probe spectroscopy. We
demonstrated that graphene exhibits semiconducting positive photoconductivity
near zero carrier density, which crosses over to metallic negative
photoconductivity at high carrier density. Our observations are accounted for
by considering the interplay between photo-induced changes of both the Drude
weight and the carrier scattering rate. Notably, we observed multiple sign
changes in the temporal photoconductivity dynamics at low carrier density. This
behavior reflects the non-monotonic temperature dependence of the Drude weight,
a unique property of massless Dirac fermions
Pairing without Superfluidity: The Ground State of an Imbalanced Fermi Mixture
Radio-frequency spectroscopy is used to study pairing in the normal and
superfluid phases of a strongly interacting Fermi gas with imbalanced spin
populations. At high spin imbalances the system does not become superfluid even
at zero temperature. In this normal phase full pairing of the minority atoms is
observed. This demonstrates that mismatched Fermi surfaces do not prevent
pairing but can quench the superfluid state, thus realizing a system of fermion
pairs that do not condense even at the lowest temperature
Critical phenomena in globally coupled excitable elements
Critical phenomena in globally coupled excitable elements are studied by
focusing on a saddle-node bifurcation at the collective level. Critical
exponents that characterize divergent fluctuations of interspike intervals near
the bifurcation are calculated theoretically. The calculated values appear to
be in good agreement with those determined by numerical experiments. The
relevance of our results to jamming transitions is also mentioned.Comment: 4 pages, 3 figure
Spin relaxation in mesoscopic superconducting Al wires
We studied the diffusion and the relaxation of the polarized quasiparticle
spins in superconductors. To that end, quasiparticles of polarized spins were
injected through an interface of a mesoscopic superconducting Al wire in
proximity contact with an overlaid ferromagnetic Co wire in the single-domain
state. The superconductivity was observed to be suppressed near the
spin-injecting interface, as evidenced by the occurrence of a finite voltage
for a bias current below the onset of the superconducting transition. The spin
diffusion length, estimated from finite voltages over a certain length of Al
wire near the interface, was almost temperature independent in the temperature
range sufficiently below the superconducting transition but grew as the
transition temperature was approached. This temperature dependence suggests
that the relaxation of the spin polarization in the superconducting state is
governed by the condensation of quasiparticles to the paired state. The spin
relaxation in the superconducting state turned out to be more effective than in
the normal state.Comment: 9 pages, 8 figure
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