6,403 research outputs found
Phonon driven spin distribution due to the spin-Seebeck effect
Here we report on measurements of the spin-Seebeck effect of GaMnAs over an
extended temperature range alongside the thermal conductivity, specific heat,
magnetization, and thermoelectric power. The amplitude of the spin-Seebeck
effect in GaMnAs scales with the thermal conductivity of the GaAs substrate and
the phonon-drag contribution to the thermoelectric power of the GaMnAs,
demonstrating that phonons drive the spin redistribution. A phenomenological
model involving phonon-magnon drag explains the spatial and temperature
dependence of the measured spin distribution.Comment: 12 pages, 3 figure
Quality assurance in stereotactic radiosurgery/radiotherapy according to DIN 6875-1
The new DIN (' Deutsche Industrie- Norm') 6875- 1, which is currently being finalised, deals with quality assurance ( QA) criteria and tests methods for linear accelerator and Gamma Knife stereotactic radiosurgery/ radiotherapy including treatment planning, stereotactic frame and stereotactic imaging and a system test to check the whole chain of uncertainties. Our existing QA program, based on dedicated phantoms and test procedures, has been refined to fulfill the demands of this new DIN. The radiological and mechanical isocentre corresponded within 0.2 mm and the measured 50% isodose lines were in agreement with the calculated ones within less than 0.5 mm. The measured absorbed dose was within 3%. The resultant output factors measured for the 14-, 8- and 4- mm collimator helmet were 0.9870 +/- 0.0086, 0.9578 +/- 0.0057 and 0.8741 +/- 0.0202, respectively. For 170 consecutive tests, the mean geometrical accuracy was 0.48 +/- 0.23 mm. Besides QA phantoms and analysis software developed in- house, the use of commercially available tools facilitated the QA according to the DIN 6875- 1 with which our results complied. Copyright (C) 2004 S. Karger AG, Basel
Oscillatory Spin Polarization and Magneto-Optic Kerr Effect in Fe3O4 Thin Films on GaAs(001)
The spin dependent properties of epitaxial Fe3O4 thin films on GaAs(001) are
studied by the ferromagnetic proximity polarization (FPP) effect and
magneto-optic Kerr effect (MOKE). Both FPP and MOKE show oscillations with
respect to Fe3O4 film thickness, and the oscillations are large enough to
induce repeated sign reversals. We attribute the oscillatory behavior to
spin-polarized quantum well states forming in the Fe3O4 film. Quantum
confinement of the t2g states near the Fermi level provides an explanation for
the similar thickness dependences of the FPP and MOKE oscillations.Comment: to appear in Phys. Rev. Let
NASA Manned Launch Vehicle Lightning Protection Development
Historically, the National Aeronautics and Space Administration (NASA) relied heavily on lightning avoidance to protect launch vehicles and crew from lightning effects. As NASA transitions from the Space Shuttle to the new Constellation family of launch vehicles and spacecraft, NASA engineers are imposing design and construction standards on the spacecraft and launch vehicles to withstand both the direct and indirect effects of lightning. A review of current Space Shuttle lightning constraints and protection methodology will be presented, as well as a historical review of Space Shuttle lightning requirements and design. The Space Shuttle lightning requirements document, NSTS 07636, Lightning Protection, Test and Analysis Requirements, (originally published as document number JSC 07636, Lightning Protection Criteria Document) was developed in response to the Apollo 12 lightning event and other experiences with NASA and the Department of Defense launch vehicles. This document defined the lightning environment, vehicle protection requirements, and design guidelines for meeting the requirements. The criteria developed in JSC 07636 were a precursor to the Society of Automotive Engineers (SAE) lightning standards. These SAE standards, along with Radio Technical Commission for Aeronautics (RTCA) DO-160, Environmental Conditions and Test Procedures for Airborne Equipment, are the basis for the current Constellation lightning design requirements. The development and derivation of these requirements will be presented. As budget and schedule constraints hampered lightning protection design and verification efforts, the Space Shuttle elements waived the design requirements and relied on lightning avoidance in the form of launch commit criteria (LCC) constraints and a catenary wire system for lightning protection at the launch pads. A better understanding of the lightning environment has highlighted the vulnerability of the protection schemes and associated risk to the vehicle, which has resulted in lost launch opportunities and increased expenditures in manpower to assess Space Shuttle vehicle health and safety after lightning events at the launch pad. Because of high-percentage launch availability and long-term on-pad requirements, LCC constraints are no longer considered feasible. The Constellation vehicles must be designed to withstand direct and indirect effects of lightning. A review of the vehicle design and potential concerns will be presented as well as the new catenary lightning protection system for the launch pad. This system is required to protect the Constellation vehicles during launch processing when vehicle lightning effects protection might be compromised by such items as umbilical connections and open access hatches
Localized Endomorphisms of the Chiral Ising Model
Based on the treatment of the chiral Ising model by Mack and Schomerus, we
present examples of localized endomorphisms and
. It is shown that they lead to the same
superselection sectors as the global ones in the sense that unitary equivalence
and holds. Araki's formalism of the selfdual CAR algebra is
used for the proof. We prove local normality and extend representations and
localized endomorphisms to a global algebra of observables which is generated
by local von Neumann algebras on the punctured circle. In this framework, we
manifestly prove fusion rules and derive statistics operators.Comment: 41 pages, latex2
Construction of Field Algebras with Quantum Symmetry from Local Observables
It has been discussed earlier that ( weak quasi-) quantum groups allow for
conventional interpretation as internal symmetries in local quantum theory.
From general arguments and explicit examples their consistency with (braid-)
statistics and locality was established. This work addresses to the
reconstruction of quantum symmetries and algebras of field operators. For every
algebra \A of observables satisfying certain standard assumptions, an
appropriate quantum symmetry is found. Field operators are obtained which act
on a positive definite Hilbert space of states and transform covariantly under
the quantum symmetry. As a substitute for Bose/Fermi (anti-) commutation
relations, these fields are demonstrated to obey local braid relation.Comment: 50 pages, HUTMP 93-B33
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Double Chain Ladder and Bornhuetter-Ferguson
In this article we propose a method close to Double Chain Ladder (DCL) introduced by Martínez-Miranda, Nielsen, and Verrall (2012a). The proposed method is motivated by the potential lack of stability of the DCL method (and of the classical Chain ladder method [CLM] itself). We consider the implicit estimation of the underwriting year inflation in the CLM method and the explicit estimation of it in DCL. This may represent a weak point for DCL and CLM because the underwriting year inflation might be estimated with significant uncertainty. A key feature of the new method is that the underwriting year inflation can be estimated from the less volatile incurred data and then transferred into the DCL model. We include an empirical illustration that illustrates the differences between the estimates of the IBNR and RBNS cash flows from DCL and the new method. We also apply bootstrap estimation to approximate the predictive distributions
Epitaxial EuO Thin Films on GaAs
We demonstrate the epitaxial growth of EuO on GaAs by reactive molecular beam
epitaxy. Thin films are grown in an adsorption-controlled regime with the aid
of an MgO diffusion barrier. Despite the large lattice mismatch, it is shown
that EuO grows well on MgO(001) with excellent magnetic properties. Epitaxy on
GaAs is cube-on-cube and longitudinal magneto-optic Kerr effect measurements
demonstrate a large Kerr rotation of 0.57{\deg}, a significant remanent
magnetization, and a Curie temperature of 69 K.Comment: 5 pages, 3 figure
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