12,814 research outputs found
Spin-lattice Interaction For Ions In Low-symmetry Sites: The Case Of Mn2+:caco3
The spin-lattice interaction for Mn2+ ions as substitutional impurities in CaCO3 has been studied by electron-paramagnetic-resonance (EPR) experiments in crystals under externally applied uniaxial stresses. The shifts of the EPR lines of Mn2+ were measured as a function of the stress applied along the three different directions that accept uniaxial forces in this crystal. The values of six second-order spin-lattice coefficients for the Mn2+ site were obtained from the data. We also obtained two conditions relating linear combinations of the other four second-order coefficients. Contributions to the spin-lattice interaction of terms of fourth order in the effective spin have been detected. Our results are used to discuss the effect on the EPR spectrum of the different distortions of the carbonate ions surrounding the Mn2+. © 1994 The American Physical Society.49138583859
Resonant Axisymmetric Modes
Axisymmetric modes in shaped tokamak plasmas are normally associated with vertical displacement events. However, not enough attention has been given to the fact that these modes can be resonant in two different ways. Firstly, for a plasma bounded by a divertor separatrix, a generic n=0 ideal-MHD perturbation, ξ, is singular at the divertor X- point(s), where Beq · ∇ξ = 0, with Beq the equilibrium magnetic field. As a consequence, n=0 perturbations can give rise to current sheets localized along the divertor separatrix. Secondly, a feedback-stabilized n=0 mode tends to acquire an Alfv ́enic oscillation frequency. As a result, a resonant interaction with energetic particle orbits can lead to a new type of fast ion instability
Lie-orthogonal operators
Basic properties of Lie-orthogonal operators on a finite-dimensional Lie
algebra are studied. In particular, the center, the radical and the components
of the ascending central series prove to be invariant with respect to any
Lie-orthogonal operator. Over an algebraically closed field of characteristic
0, only solvable Lie algebras with solvability degree not greater than two
admit Lie-orthogonal operators whose all eigenvalues differ from 1 and -1. The
main result of the paper is that Lie-orthogonal operators on a simple Lie
algebra are exhausted by the trivial ones. This allows us to give the complete
description of Lie-orthogonal operators for semi-simple and reductive algebras,
as well as a preliminary description of Lie-orthogonal operators on Lie
algebras with nontrivial Levi-Mal'tsev decomposition. The sets of
Lie-orthogonal operators of some classes of Lie algebras (Heisenberg algebras,
almost Abelian algebras, etc.) are directly computed. In particular, it appears
that the group formed by the equivalence classes of Lie-orthogonal operators on
a Heisenberg algebra is isomorphic to the standard symplectic group of an
appropriate dimension.Comment: 17 pages, minor improvements have been mad
AC-coupled GaAs microstrip detectors with a new type of integrated bias resistors
Full size single-sided GaAs microstrip detectors with integrated coupling
capacitors and bias resistors have been fabricated on 3'' substrate wafers.
PECVD deposited SiO_2 and SiO_2/Si_3N_4 layers were used to provide coupling
capacitaces of 32.5 pF/cm and 61.6 pF/cm, respectively. The resistors are made
of sputtered CERMET using simple lift of technique. The sheet resistivity of 78
kOhm/sq. and the thermal coefficient of resistance of less than 4x10^-3 /
degree C satisfy the demands of small area biasing resistors, working on a wide
temperature range.Comment: 20 pages, 9 figures, to be published in NIM
Characterization of As-polluted soils by laboratory X-ray-based techniques coupled with sequential extractions and electron microscopy: the case of Crocette gold mine in the Monte Rosa mining district (Italy)
Arsenic concentration and distribution were studied by combining laboratory X-ray-based techniques (wavelength dispersive X-ray fluorescence (WDXRF), micro X-ray fluorescence (μXRF), and X-ray powder diffraction (XRPD)), field emission scanning electron microscopy equipped with microanalysis (FE-SEM-EDX), and sequential extraction procedure (SEP) coupled to total reflection X-ray fluorescence (TXRF) analysis. This approach was applied to three contaminated soils and one mine tailing collected near the gold extraction plant at the Crocette gold mine (Macugnaga, VB) in the Monte Rosa mining district (Piedmont, Italy). Arsenic (As) concentration, measured with WDXRF, ranged from 145 to 40,200 mg/kg. XRPD analysis evidenced the presence of jarosite and the absence of any As-bearing mineral, suggesting a high weathering grade and strong oxidative conditions. However, small domains of Fe arsenate were identified by combining μXRF with FE-SEM-EDX. SEP results revealed that As was mainly associated to amorphous Fe oxides/hydroxides or hydroxysulfates (50–80%) and the combination of XRPD and FE-SEM-EDX suggested that this phase could be attributed to schwertmannite. On the basis of the reported results, As is scarcely mobile, even if a consistent As fraction (1–3 g As/kg of soil) is still potentially mobilizable. In general, the proposed combination of laboratory X-ray techniques could be successfully employed to unravel environmental issues related to metal(loid) pollution in soil and sediments
Interpretation of the Theta+ as an isotensor pentaquark with weakly decaying partners
The Theta+(1540), recently observed at LEPS, DIANA and CLAS, is hypothesized
to be an isotensor resonance. This implies the existence of a multiplet where
the Theta++, Theta+ and Theta0 have isospin-violating strong decays, and the
Theta+++ and Theta- have weak decays and so are long-lived. Production
mechanisms for these states are discussed. The J^P assignment of the Theta is
most likely 1/2^- or 3/2^-.Comment: references added, section on pentaquark model revised, 11 pages,
LaTeX, accepted for publication in Physics Letters
Impact of Investor's Varying Risk Aversion on the Dynamics of Asset Price Fluctuations
While the investors' responses to price changes and their price forecasts are
well accepted major factors contributing to large price fluctuations in
financial markets, our study shows that investors' heterogeneous and dynamic
risk aversion (DRA) preferences may play a more critical role in the dynamics
of asset price fluctuations. We propose and study a model of an artificial
stock market consisting of heterogeneous agents with DRA, and we find that DRA
is the main driving force for excess price fluctuations and the associated
volatility clustering. We employ a popular power utility function,
with agent specific and
time-dependent risk aversion index, , and we derive an approximate
formula for the demand function and aggregate price setting equation. The
dynamics of each agent's risk aversion index, (i=1,2,...,N), is
modeled by a bounded random walk with a constant variance . We show
numerically that our model reproduces most of the ``stylized'' facts observed
in the real data, suggesting that dynamic risk aversion is a key mechanism for
the emergence of these stylized facts.Comment: 17 pages, 7 figure
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