576 research outputs found
Orbital-Order Driven Ferroelectricity and Dipolar Relaxation Dynamics in Multiferroic GaMoS
We present the results of broadband dielectric spectroscopy of GaMoS,
a lacunar spinel system that recently was shown to exhibit non-canonical,
orbitally-driven ferroelectricity. Our study reveals complex relaxation
dynamics of this multiferroic material, both above and below its Jahn-Teller
transition at T K. Above T, two types of
coupled dipolar-orbital dynamics seem to compete: relaxations within
cluster-like regions with short-range polar order like in relaxor
ferroelectrics and critical fluctuations of only weakly interacting dipoles,
the latter resembling the typical dynamics of order-disorder type
ferroelectrics. Below the Jahn-Teller transition, the onset of orbital order
drives the system into long-range ferroelectric order and dipolar dynamics
within the ferroelectric domains is observed. The coupled dipolar and orbital
relaxation behavior of GaMoS above the Jahn-Teller transition markedly
differs from that of the skyrmion host GaVS, which seems to be linked
to differences in the structural distortions of the two systems on the
unit-cell level.Comment: 6 pages, 3 figures + Supplemental Material (2 pages, 2 figures
Equilibrium configurations for quark-diquark stars and the problem of Her X-1 mass
We report new calculations of the physical properties of a quark-diquark
plasma. A vacuum contribution is taken into account and is responsible for the
appearance of a stable state at zero pressure and at a baryon density of about
2.2 times the nuclear matter density in this model. The resulting equation of
state was used to integrate numerically the Tolman-Oppenheimer-Volkoff
equations. The mass-radius relationship has been derived from a series of
equilibrium configurations constituted by a mixture of quarks and diquarks.
These stellar models, which are representative of a whole class, may be helpful
to understand the possible compactness of the X-ray source Her X-1 and related
objects.Comment: 15 pp., PlainTex file + 3 figures available upon request at
[email protected]. Submitted to Int. Jour. Mod. Phys.
Stroboscopic Laser Diagnostics for Detection of Ordering in One-Dimensional Ion beam
A novel diagnostic method for detecting ordering in one-dimensional ion beams
is presented. The ions are excited by a pulsed laser at two different positions
along the beam and fluorescence is observed by a group of four
photomultipliers. Correlation in fluorescence signals is firm indication that
the ion beam has an ordered structure.Comment: 7 pages, REVTEX, fig3 uuencoded, figs 1-2 available upon request from
[email protected], to appear in Phys. Rev.
H-NMR Study of the Random Bond Effect in the Quantum Spin System (CH)CHNHCu(ClBr)
Spin-lattice relaxation rate of H-NMR has been measured in
(CH)CHNHCu(ClBr) with , which has been
reported to be gapped system with singlet ground state from the previous
macroscopic magnetization and specific heat measurements, in order to
investigate the bond randomness effect microscopically in the gapped composite
Haldane system (CH)CHNHCuCl. It was found that the spin-lattice
relaxation rate in the present system includes both fast and slow
relaxation parts indicative of the gapless magnetic ground state and the gapped
singlet ground state, respectively. We discuss the obtained results with the
previous macroscopic magnetization and specific heat measurements together with
the microscopic SR experiments.Comment: 4 pages, 2 figures, to be published in J. Phys. Soc. Jpn. vol.76
(2007) No.
Critical Phenomena in Long-Range RKKY Ising Spin Glasses
We have investigated critical phenomena in spin glasses RxY1-xRu2Si2 (R = Dy,
Tb, Gd). These compounds, where the magnetic moments of rare-earth ions
interact by the long-range Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction
via conduction electrons, has uniaxial magnetic anisotropy. The separation of
the zero-field-cooled and field-cooled magnetization was found only along the
c-axis in all compounds, and hence, they are classified into the long-range
Ising spin glass. The magnetic anisotropic energies in these compounds are
different from each other in two orders of magnitude, from 330 K to 1.8 K,
however, the critical exponents are similar. It clearly indicates a presence of
the universality of the long-range RKKY Ising spin glasses.Comment: 6 pages, 3 figures, Proceedings of ICFCM 201
Superconductivity in a layered cobalt oxyhydrate NaCoO1.3HO
We report the electrical, magnetic and thermal measurements on a layered
cobalt oxyhydrate NaCoO1.3HO. Bulk superconductivity
at 4.3 K has been confirmed, however, the measured superconducting fraction is
relatively low probably due to the sample's intrinsic two-dimensional
characteristic. The compound exhibits weak-coupled and extreme type-II
superconductivity with the average energy gap and the
Ginzburg-Landau parameter of 0.50 meV and 140,
respectively. The normalized electronic specific heat data in the
superconducting state well fit the dependence, suggesting point nodes
for the superconducting gap structure.Comment: 4 pages, 3 figure
A Remarkable Three Hour Thermonuclear Burst From 4U 1820-30
We present a detailed observational and theoretical study of a ~3 hr long
X-ray burst (the ``super burst'') observed by the Rossi X-ray Timing Explorer
(RXTE) from the low mass X-ray binary (LMXB) 4U 1820-30. This is the longest
X-ray burst ever observed from this source, and perhaps one of the longest ever
observed in great detail from any source. We show that the super burst is
thermonuclear in origin. The level of the accretion driven flux as well as the
total energy release of ~1.5 x 10^{42} ergs indicate that helium could not be
the energy source for the super burst. We outline the physics relevant to
carbon production and burning on helium accreting neutron stars and present
calculations of the thermal evolution and stability of a carbon layer and show
that this process is the most likely explanation for the super burst. We show
that for large columns of accreted carbon fuel, a substantial fraction of the
energy released in the carbon burning layer is radiated away as neutrinos, and
the heat that is conducted from the burning layer in large part flows inward,
only to be released on timescales longer than the observed burst. Thus the
energy released possibly exceeds that observed in X-rays by more than a factor
of ten. Spectral analysis during the super burst reveals the presence of a
broad emission line between 5.8 - 6.4 keV and an edge at 8 - 9 keV likely due
to reflection of the burst flux from the inner accretion disk in 4U 1820-30. We
believe this is the first time such a signature has been unambiguously detected
in the spectrum of an X-ray burst.Comment: AASTEX, 44 pages, 14 figures. Accepted for publication in the
Astrophysical Journa
Higher IL-10 levels are associated with less effective clearance of Plasmodium falciparum parasites
The implications of high levels of the immune regulatory cytokine IL-10 in Plasmodium falciparum malaria are unclear. IL-10 may down-regulate pro-inflammatory responses and also exacerbate disease by inhibiting anti-parasitic immune functions. To study possible inhibiting effects on parasite clearance, IL-10 plasma levels were determined in 104 Tanzanian children, 1 to 4 years old, with acute uncomplicated P. falciparum malaria, and analysed for association with parasite densities during 3 days of anti-malarial treatment. Higher baseline IL-10 plasma levels were associated with statistically significantly higher parasite densities after 24, 48 and 72 h of treatment. These associations could not be explained by differences in initial parasitaemia, temperature, age, sex or type of treatment. Induction of high IL-10 production might be a direct or indirect mechanism whereby the parasite evades the immune response
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