24,901 research outputs found
Ferroelectric Dynamics in the Perovskite Relaxor PMN
We review results obtained from recent neutron scattering studies of the
lead-oxide class of perovskite relaxors PMN and PZN. A ferroelectric soft mode
has been identified in PMN at 1100 K that becomes overdamped near 620 K. This
is the same temperature at which polar nanoregions (PNR) begin to form, denoted
by Td, and suggests that a direct connection exists between the soft mode and
the PNR. The appearance of diffuse scattering intensity at Td reported by
Naberezhnov et al. lends further support to this picture. At lower temperature
the soft mode in PMN reappears close to Tc = 213 K (defined only for E > Ec).
These results are provocative because the dynamics below Tc are characteristic
of an ordered ferroelectric state, yet they occur in a system that remains
cubic on average at all temperatures. We discuss a coupled-mode model that
successfully describes these data as well as those from earlier lattice
dynamical studies of other perovskites such as BaTiO3.Comment: 10 pages, 7 figures, Conference - Fundamental Physics of
Ferroelectrics 200
Fractional exclusion and braid statistics in one dimension: a study via dimensional reduction of Chern-Simons theory
The relation between braid and exclusion statistics is examined in
one-dimensional systems, within the framework of Chern-Simons statistical
transmutation in gauge invariant form with an appropriate dimensional
reduction. If the matter action is anomalous, as for chiral fermions, a
relation between braid and exclusion statistics can be established explicitly
for both mutual and nonmutual cases. However, if it is not anomalous, the
exclusion statistics of emergent low energy excitations is not necessarily
connected to the braid statistics of the physical charged fields of the system.
Finally, we also discuss the bosonization of one-dimensional anyonic systems
through T-duality.Comment: 19 pages, fix typo
Acoustic Attenuation by Two-dimensional Arrays of Rigid Cylinders
In this Letter, we present a theoretical analysis of the acoustic
transmission through two-dimensional arrays of straight rigid cylinders placed
parallelly in the air. Both periodic and completely random arrangements of the
cylinders are considered. The results for the sound attenuation through the
periodic arrays are shown to be in a remarkable agreement with the reported
experimental data. As the arrangement of the cylinders is randomized, the
transmission is significantly reduced for a wider range of frequencies. For the
periodic arrays, the acoustic band structures are computed by the plane-wave
expansion method and are also shown to agree with previous results.Comment: 4 pages, 3 figure
Hydrostatic pressure effects on the static magnetism in Eu(FeCo)As
The effects of hydrostatic pressure on the static magnetism in
Eu(FeCo)As are investigated by complementary
electrical resistivity, ac magnetic susceptibility and single-crystal neutron
diffraction measurements. A specific pressure-temperature phase diagram of
Eu(FeCo)As is established. The structural phase
transition, as well as the spin-density-wave order of Fe sublattice, is
suppressed gradually with increasing pressure and disappears completely above
2.0 GPa. In contrast, the magnetic order of Eu sublattice persists over the
whole investigated pressure range up to 14 GPa, yet displaying a non-monotonic
variation with pressure. With the increase of the hydrostatic pressure, the
magnetic state of Eu evolves from the canted antiferromagnetic structure in the
ground state, via a pure ferromagnetic structure under the intermediate
pressure, finally to a possible "novel" antiferromagnetic structure under the
high pressure. The strong ferromagnetism of Eu coexists with the
pressure-induced superconductivity around 2 GPa. The change of the magnetic
state of Eu in Eu(FeCo)As upon the application
of hydrostatic pressure probably arises from the modification of the indirect
Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between the Eu moments
tuned by external pressure.Comment: 9 pages, 6 figure
Interaction of HIV protease inhibitors with OATP1B1, 1B3, and 2B1
The effects of human immunodeficiency virus (HIV) protease inhibitors (PI) on the accumulation of the fluorescent bile salt analogue cholyl-glycylamido-fluorescein (CGamF) were determined in organic anion transporting polypeptide (OATP)-1B1 and -1B3-expressing Chinese hamster ovary (CHO) cells. In addition, interaction studies in Caco-2 monolayers, known only to express the OATP2B1 isoform, were conducted using the established OATP substrate estrone 3-sulfate (E3S), since no CGamF accumulation was observed in Caco-2 monolayers. CGamF appeared an excellent substrate for the OATP1B subfamily, with net accumulation clearance values of 7.8 and 142 microl min(-1) mg(-1) protein in OATP1B1 and OATP1B3-transfected cells, respectively. K(i)-values reflecting inhibition of CGamF accumulation by HIV PI correlated well between OATP1B1 and OATP1B3-expressing cells. Lopinavir was the most potent inhibitor (K(i) = 0.5-1.4 microM) of OATP1B-mediated CGamF accumulation compared with atazanavir, darunavir, ritonavir, and saquinavir (K(i) between 1.4 and 3.3 microM). Inhibitory profiles towards OATP2B1-mediated E3S accumulation were different with only indinavir, saquinavir, and ritonavir showing substantial effects. In conclusion, OATP1B3 appears to be a major transport mechanism mediating sodium-independent CGamF accumulation in human liver, and CGamF could be used as a probe substrate for in vitro drug interaction studies. The remarkably potent inhibition of OATP1B1 by lopinavir may explain some clinically relevant drug interactions between lopinavir and OATP1B substrates such as fexofenadine
Soft Mode Dynamics Above and Below the Burns Temperature in the Relaxor Pb(Mg_1/3Nb_2/3)O_3
We report neutron inelastic scattering measurements of the lowest-energy
transverse optic (TO) phonon branch in the relaxor Pb(Mg_1/3Nb_2/3)O_3 from 400
to 1100 K. Far above the Burns temperature T_d ~ 620 K we observe well-defined
propagating TO modes at all wave vectors q, and a zone center TO mode that
softens in a manner consistent with that of a ferroelectric soft mode. Below
T_d the zone center TO mode is overdamped. This damping extends up to, but not
above, the waterfall wave vector q_wf, which is a measure of the average size
of the PNR.Comment: 4 pages, 4 figures; modified discussion of Fig. 3, shortened
captions, added reference, corrected typos, accepted by Phys. Rev. Let
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