10,942 research outputs found
Non-cyclic Geometric Phase due to Spatial Evolution in a Neutron Interferometer
We present a split-beam neutron interferometric experiment to test the
non-cyclic geometric phase tied to the spatial evolution of the system: the
subjacent two-dimensional Hilbert space is spanned by the two possible paths in
the interferometer and the evolution of the state is controlled by phase
shifters and absorbers. A related experiment was reported previously by
Hasegawa et al. [Phys. Rev. A 53, 2486 (1996)] to verify the cyclic spatial
geometric phase. The interpretation of this experiment, namely to ascribe a
geometric phase to this particular state evolution, has met severe criticism
from Wagh [Phys. Rev. A 59, 1715 (1999)]. The extension to a non-cyclic
evolution manifests the correctness of the interpretation of the previous
experiment by means of an explicit calculation of the non-cyclic geometric
phase in terms of paths on the Bloch-sphere.Comment: 4 pages, revtex
Dynamics of the Tippe Top -- properties of numerical solutions versus the dynamical equations
We study the relationship between numerical solutions for inverting Tippe Top
and the structure of the dynamical equations. The numerical solutions confirm
oscillatory behaviour of the inclination angle for the symmetry
axis of the Tippe Top. They also reveal further fine features of the dynamics
of inverting solutions defining the time of inversion. These features are
partially understood on the basis of the underlying dynamical equations
Comparative survey of dynamic analyses of free-piston Stirling engines
Reported dynamics analyses for evaluating the steady-state response and stability of free-piston Stirling engine (FPSE) systems are compared. Various analytical approaches are discussed to provide guidance on their salient features. Recommendations are made in the recommendations remarks for an approach which captures most of the inherent properties of the engine. Such an approach has the potential for yielding results which will closely match practical FPSE-load systems
Non-LTE spectral models for the gaseous debris-disk component of Ton 345
For a fraction of single white dwarfs with debris disks, an additional
gaseous disk was discovered. Both dust and gas are thought to be created by the
disruption of planetary bodies. The composition of the extrasolar planetary
material can directly be analyzed in the gaseous disk component, and the disk
dynamics might be accessible by investigating the temporal behavior of the Ca
II infrared emission triplet, hallmark of the gas disk.
We obtained new optical spectra for the first helium-dominated white dwarf
for which a gas disk was discovered (Ton 345) and modeled the non-LTE spectra
of viscous gas disks composed of carbon, oxygen, magnesium, silicon, sulfur,
and calcium with chemical abundances typical for solar system asteroids. Iron
and its possible line-blanketing effects on the model structure and spectral
energy distribution was still neglected. A set of models with different radii,
effective temperatures, and surface densities as well as chondritic and
bulk-Earth abundances was computed and compared with the observed line profiles
of the Ca II infrared triplet.
Our models suggest that the Ca II emission stems from a rather narrow gas
ring with a radial extent of R=0.44-0.94 Rsol, a uniform surface density
Sigma=0.3 g/cm2, and an effective temperature of Teff=6000 K. The often assumed
chemical mixtures derived from photospheric abundances in polluted white dwarfs
- similar to a chondritic or bulk-Earth composition - produce unobserved
emission lines in the model and therefore have to be altered. We do not detect
any line-profile variability on timescales of hours, but we confirm the
long-term trend over the past decade for the red-blue asymmetry of the
double-peaked lines.Comment: 7 pages, 6 figures, 2 table
Transformation toughened ceramics for the heavy duty diesel engine technology program
The objective of this program is to develop an advanced high temperature oxide structural ceramic for application to the heavy duty diesel engine. The approach is to employ transformation toughening by additions of ZrO.5HfO.5O2 solid solution to the oxide ceramics, mullite (2Al2O3S2SiO2) and alumina (Al2O3). The study is planned for three phases, each 12 months in duration. This report covers Phase 1. During this period, processing techniques were developed to incorporate the ZrO.5HfO.5O2 solid solution in the matrices while retaining the necessary metastable tetragonal phase. Modulus of rupture and of elasticity, coefficient of thermal expansion, fracture toughness by indent technique and thermal diffusivity of representative specimens were measured. In Phase 2, the process will be improved to provide higher mechanical strength and to define the techniques for scale up to component size. In Phase 3, full scale component prototypes will be fabri-]cated
Asymmetric Line Profiles in Spectra of Gaseous Metal Disks Around Single White Dwarfs
Around several single DAZ and DBZ white dwarfs metal-rich disks have been
observed, which are mostly believed to originate from disruption of smaller
rocky planetesimals. In some cases the material does not (only) form a dusty
but gaseous disk. In the case of SDSS J122859.93+104032.9 the double peaked
infrared Ca II triplet at about 8500 angstrom, one of only two emission
features of the spectra, exhibits a strong red/violet asymmetry. Assuming a
composition similar to a chondrite-like asteroid, being the most prominent type
in our own solar system, we calculated the spectrum and vertical structure of
the disk using the Tuebingen NLTE accretion disk code "AcDc". Modified to
simulate different non axis-symmetrical disk geometries, the first preliminary
results are in good agreement with the observed asymmetric line profile.Comment: 6 pages, 5 figures, proceeding of the "17th European White Dwarf
Workshop", Tuebingen, Germany, 201
Reconsidering post-war narratives of involvement in Nazi violence
In this article, I will develop an approach to utilizing narrative interviews with individuals who witnessed, became complicit in, facilitated, or benefitted from National Socialist violence. Drawing on a collection of recent interviews by a documentary filmmaker, I will demonstrate the importance of the context of their co-production and their socio-political and cultural embeddedness. By analyzing them as cultural artefacts of a particular time and place, I will identify a rise in anxiety in approaching Germans and Austrians on the side of persecutors and the appropriation of the figure of the contemporary witness or Zeitzeuge as practice, performance, discursive strategy, and subject position
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