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NWA 6356: unequilibrated polymict ureilite
Polymict ureilite NWA 6356 has not suffered an intensive metamorphism and keeps the evidence of multistage carbon injections, reducing sulphuric metasomatism, and consists of feldspathic clasts and best preserved CM-like chondrite fragments
The fission yeast FANCM ortholog directs non-crossover recombination during meiosis
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Origin of the ungrouped achondrite NWA 4518: mineralogy and geochemistry of FeNi-metal
Ungrouped achondrite NWA 4518 is an ultramafic breccia with abundant siderophile rich IIA-like metal. Its silicate chemistry is similar to that of WINs, HEDs, and silicate inclusions of IIE irons. Oxygen isotopic composition is nearby IAB-IIICD-WIN
Magnetostrictive Neel ordering of the spin-5/2 ladder compound BaMn2O3: distortion-induced lifting of geometrical frustration
The crystal structure and the magnetism of BaMnO have been studied by
thermodynamic and by diffraction techniques using large single crystals and
powders. BaMnO is a realization of a spin ladder as the
magnetic interaction is dominant along 180 Mn-O-Mn bonds forming the
legs and the rungs of a ladder. The temperature dependence of the magnetic
susceptibility exhibits well-defined maxima for all directions proving the
low-dimensional magnetic character in BaMnO. The susceptibility and
powder neutron diffraction data, however, show that BaMnO exhibits a
transition to antiferromagnetic order at 184 K, in spite of a full frustration
of the nearest-neighbor inter-ladder coupling in the orthorhombic
high-temperature phase. This frustration is lifted by a remarkably strong
monoclinic distortion which accompanies the magnetic transition.Comment: 9 pages, 8 figures, 2 tables; in V1 fig. 2 was included twice and
fig. 4 was missing; this has been corrected in V
A Field-Induced Re-Entrant Novel Phase and A Ferroelectric-Magnetic Order Coupling in HoMnO3
A re-entrant novel phase has been observed in the hexagonal ferroelectric
HoMnO3 in the presence of magnetic fields, in the temperature ranges defined by
the plateau of the dielectric constant anomaly. The dielectric plateau evolves
with fields from a narrow sharp dielectric peak at the Mn-spin rotation
transition at 32.8 K in zero magnetic field. Such a field-induced dielectric
plateau anomaly appears both in the temperature sweep at a constant field and
in the field sweep at a constant temperature without detectable hysteresis.
This is attributed to the indirect coupling between the ferroelectric and
antiferromagnetic orders, arising from an antiferromagnetic domain wall effect,
where the magnetic order parameter of the Mn subsystem has to change sign
across the ferroelectric domain wall in the compound, that influences the
ferroelectric domains via a local magnetostrictive effect
The Active Mirror Control of the MAGIC Telescope
One of the main design goals of the MAGIC telescopes is the very fast
repositioning in case of Gamma Ray Burst (GRB) alarms, implying a low weight of
the telescope dish. This is accomplished by using a space frame made of carbon
fiber epoxy tubes, resulting in a strong but not very rigid support structure.
Therefore it is necessary to readjust the individual mirror tiles to correct
for deformations of the dish under varying gravitational load while tracking an
object. We present the concept of the Active Mirror Control (AMC) as
implemented in the MAGIC telescopes and the actual performance reached.
Additionally we show that also telescopes using a stiff structure can benefit
from using an AMC.Comment: Contribution to the 30th ICRC, Merida, Mexico, July 2007 on behalf of
the MAGIC Collaboratio
Improved linear response for stochastically driven systems
The recently developed short-time linear response algorithm, which predicts
the average response of a nonlinear chaotic system with forcing and dissipation
to small external perturbation, generally yields high precision of the response
prediction, although suffers from numerical instability for long response times
due to positive Lyapunov exponents. However, in the case of stochastically
driven dynamics, one typically resorts to the classical fluctuation-dissipation
formula, which has the drawback of explicitly requiring the probability density
of the statistical state together with its derivative for computation, which
might not be available with sufficient precision in the case of complex
dynamics (usually a Gaussian approximation is used). Here we adapt the
short-time linear response formula for stochastically driven dynamics, and
observe that, for short and moderate response times before numerical
instability develops, it is generally superior to the classical formula with
Gaussian approximation for both the additive and multiplicative stochastic
forcing. Additionally, a suitable blending with classical formula for longer
response times eliminates numerical instability and provides an improved
response prediction even for long response times
Reversible skew laurent polynomial rings and deformations of poisson automorphisms
A skew Laurent polynomial ring S = R[x(+/- 1); alpha] is reversible if it has a reversing automorphism, that is, an automorphism theta of period 2 that transposes x and x(-1) and restricts to an automorphism gamma of R with gamma = gamma(-1). We study invariants for reversing automorphisms and apply our methods to determine the rings of invariants of reversing automorphisms of the two most familiar examples of simple skew Laurent polynomial rings, namely a localization of the enveloping algebra of the two-dimensional non-abelian solvable Lie algebra and the coordinate ring of the quantum torus, both of which are deformations of Poisson algebras over the base field F. Their reversing automorphisms are deformations of Poisson automorphisms of those Poisson algebras. In each case, the ring of invariants of the Poisson automorphism is the coordinate ring B of a surface in F-3 and the ring of invariants S-theta of the reversing automorphism is a deformation of B and is a factor of a deformation of F[x(1), x(2), x(3)] for a Poisson bracket determined by the appropriate surface
Development of aluminum alloy compounds for electroluminescent light sources
Aluminum alloy compounds as wide band gap semiconductors for electroluminescent light source
Impact of strong disorder on the static magnetic properties of the spin-chain compound BaCu2SiGeO7
The disordered quasi-1D magnet BaCu2SiGeO7 is considered as one of the best
physical realizations of the random Heisenberg chain model, which features an
irregular distribution of the exchange parameters and whose ground state is
predicted to be the scarcely investigated random-singlet state (RSS). Based on
extensive 29Si NMR and magnetization studies of BaCu2SiGeO7, combined with
numerical Quantum Monte Carlo simulations, we obtain remarkable quantitative
agreement with theoretical predictions of the random Heisenberg chain model and
strong indications for the formation of a random-singlet state at low
temperatures in this compound. As a local probe, NMR is a well-adapted
technique for studying the magnetism of disordered systems. In this case it
also reveals an additional local transverse staggered field (LTSF), which
affects the low-temperature properties of the RSS. The proposed model
Hamiltonian satisfactorily accounts for the temperature dependence of the NMR
line shapes.Comment: 10 pages, 7 figure
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