363 research outputs found
Nb3Sn wire shape and cross sectional area inhomogeneity in Rutherford cables
During Rutherford cable production the wires are plastically deformed and
their initially round shape is distorted. Using X-ray absorption tomography we
have determined the 3D shape of an unreacted Nb3Sn 11 T dipole Rutherford
cable, and of a reacted and impregnated Nb3Sn cable double stack.
State-of-the-art image processing was applied to correct for tomographic
artefacts caused by the large cable aspect ratio, for the segmentation of the
individual wires and subelement bundles inside the wires, and for the
calculation of the wire cross sectional area and shape variations. The 11 T
dipole cable cross section oscillates by 2% with a frequency of 1.24 mm (1/80
of the transposition pitch length of the 40 wire cable). A comparatively
stronger cross sectional area variation is observed in the individual wires at
the thin edge of the keystoned cable where the wire aspect ratio is largest.Comment: 6 pages, 11 figures, presented at EUCAS 201
Magnetization of noncircular quantum dots
We calculate the magnetization of quantum dots deviating from circular
symmetry for noninteracting electrons or electrons interacting according to the
Hartree approximation. For few electrons the magnetization is found to depend
on their number, and the shape of the dot. The magnetization is an ideal probe
into the many-electron state of a quantum dot.Comment: 11 RevTeX pages with 6 included Postscript figure
Incommensurate ground state of double-layer quantum Hall systems
Double-layer quantum Hall systems possess interlayer phase coherence at
sufficiently small layer separations, even without interlayer tunneling. When
interlayer tunneling is present, application of a sufficiently strong in-plane
magnetic field drives a commensurate-incommensurate (CI)
transition to an incommensurate soliton-lattice (SL) state. We calculate the
Hartree-Fock ground-state energy of the SL state for all values of
within a gradient approximation, and use it to obtain the
anisotropic SL stiffness, the Kosterlitz-Thouless melting temperature for the
SL, and the SL magnetization. The in-plane differential magnetic susceptibility
diverges as when the CI transition is approached
from the SL state.Comment: 12 pages, 7 figures, to be published in Physical Review
Ernst equation and spheroidal coordinates with a cosmological constant term
We discuss solution generating techniques treating stationary and axially
symmetric metrics in the presence of a cosmological constant. Using the
recently found extended form of Ernst's complex equation, which takes into
account the cosmological constant term, we propose an extension of spheroidal
coordinates adapted to asymptotically de-Sitter and anti de-Sitter static
spacetimes. In the absence of a cosmological constant we show in addition that
any higher dimensional metric parametrised by a single angular momentum can be
given by a 4 dimensional solution and Weyl potentials parametrising the extra
Killing directions. We explicitly show how a stationary, and a static axially
symmetric spacetime solution in 4 dimensions, can be {\it added} together to
give a 5 dimensional stationary and axisymmetric solution.Comment: 9 pages, no figures, some additional results to gr-qc/0610091.
Prepared for 12th Conference on Recent Developments in Gravity (NEB XII),
Nafplio, Greece, 29 Jun - 2 Jul 200
Exact relativistic treatment of stationary counter-rotating dust disks I: Boundary value problems and solutions
This is the first in a series of papers on the construction of explicit
solutions to the stationary axisymmetric Einstein equations which describe
counter-rotating disks of dust. These disks can serve as models for certain
galaxies and accretion disks in astrophysics. We review the Newtonian theory
for disks using Riemann-Hilbert methods which can be extended to some extent to
the relativistic case where they lead to modular functions on Riemann surfaces.
In the case of compact surfaces these are Korotkin's finite gap solutions which
we will discuss in this paper. On the axis we establish for general genus
relations between the metric functions and hence the multipoles which are
enforced by the underlying hyperelliptic Riemann surface. Generalizing these
results to the whole spacetime we are able in principle to study the classes of
boundary value problems which can be solved on a given Riemann surface. We
investigate the cases of genus 1 and 2 of the Riemann surface in detail and
construct the explicit solution for a family of disks with constant angular
velocity and constant relative energy density which was announced in a previous
Physical Review Letter.Comment: 32 pages, 1 figure, to appear in Phys. Rev.
Analytical approximation of the exterior gravitational field of rotating neutron stars
It is known that B\"acklund transformations can be used to generate
stationary axisymmetric solutions of Einstein's vacuum field equations with any
number of constants. We will use this class of exact solutions to describe the
exterior vacuum region of numerically calculated neutron stars. Therefore we
study how an Ernst potential given on the rotation axis and containing an
arbitrary number of constants can be used to determine the metric everywhere.
Then we review two methods to determine those constants from a numerically
calculated solution. Finally, we compare the metric and physical properties of
our analytic solution with the numerical data and find excellent agreement even
for a small number of parameters.Comment: 9 pages, 10 figures, 3 table
OBDD-Based Representation of Interval Graphs
A graph can be described by the characteristic function of the
edge set which maps a pair of binary encoded nodes to 1 iff the nodes
are adjacent. Using \emph{Ordered Binary Decision Diagrams} (OBDDs) to store
can lead to a (hopefully) compact representation. Given the OBDD as an
input, symbolic/implicit OBDD-based graph algorithms can solve optimization
problems by mainly using functional operations, e.g. quantification or binary
synthesis. While the OBDD representation size can not be small in general, it
can be provable small for special graph classes and then also lead to fast
algorithms. In this paper, we show that the OBDD size of unit interval graphs
is and the OBDD size of interval graphs is $O(\
| V \ | \log \ | V \ |)\Omega(\ | V \ | \log
\ | V \ |)O(\log \ | V \ |)O(\log^2 \ | V \ |)$ operations and
evaluate the algorithms empirically.Comment: 29 pages, accepted for 39th International Workshop on Graph-Theoretic
Concepts 201
The angular momentum and mass formulas for rotating stationary quasi-black holes
We consider the quasi-black hole limit of a stationary body when its boundary
approaches its own gravitational radius, i.e., its quasi-horizon. It is shown
that there exists a perfect correspondence between the different mass
contributions and the mass formula for quasi-black and black holes in spite of
difference in derivation and meaning of the formulas in both cases. For
extremal quasi-black holes the finite surface stresses give zero contribution
to the total mass. Conclusions similar to those for the properties of mass are
derived for the angular momentum.Comment: 14 page
Symmetries and Asymmetries of B -> K* mu+ mu- Decays in the Standard Model and Beyond
The rare decay B -> K* (-> K pi) mu+ mu- is regarded as one of the crucial
channels for B physics as the polarization of the K* allows a precise angular
reconstruction resulting in many observables that offer new important tests of
the Standard Model and its extensions. These angular observables can be
expressed in terms of CP-conserving and CP-violating quantities which we study
in terms of the full form factors calculated from QCD sum rules on the
light-cone, including QCD factorization corrections. We investigate all
observables in the context of the Standard Model and various New Physics
models, in particular the Littlest Higgs model with T-parity and various MSSM
scenarios, identifying those observables with small to moderate dependence on
hadronic quantities and large impact of New Physics. One important result of
our studies is that new CP-violating phases will produce clean signals in
CP-violating asymmetries. We also identify a number of correlations between
various observables which will allow a clear distinction between different New
Physics scenarios.Comment: 56 pages, 18 figures, 14 tables. v5: Missing factor in eqs. (3.31-32)
and fig. 6 corrected. Minor misprints in eq. (2.10) and table A corrected.
Conclusions unchange
Magnetization of a two-dimensional electron gas with a second filled subband
We have measured the magnetization of a dual-subband two-dimensional electron
gas, confined in a GaAs/AlGaAs heterojunction. In contrast to two-dimensional
electron gases with a single subband, we observe non-1/B-periodic, triangularly
shaped oscillations of the magnetization with an amplitude significantly less
than per electron. All three effects are explained by a
field dependent self-consistent model, demonstrating the shape of the
magnetization is dominated by oscillations in the confining potential.
Additionally, at 1 K, we observe small oscillations at magnetic fields where
Landau-levels of the two different subbands cross.Comment: 4 pages, 4 figure
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