1,090 research outputs found
Anderson Localization in a String of Microwave Cavities
The field distributions and eigenfrequencies of a microwave resonator which
is composed of 20 identical cells have been measured. With external screws the
periodicity of the cavity can be perturbed arbitrarily. If the perturbation is
increased a transition from extended to localized field distributions is
observed. For very large perturbations the field distributions show signatures
of Anderson localization, while for smaller perturbations the field
distribution is extended or weakly localized. The localization length of a
strongly localized field distribution can be varied by adjusting the
penetration depth of the screws. Shifts in the frequency spectrum of the
resonator provide further evidence for Anderson localization.Comment: 7 pages RevTex, to be published in Phys. Rev.
Mode Fluctuation Distribution for Spectra of Superconducting Microwave Billiards
High resolution eigenvalue spectra of several two- and three-dimensional
superconducting microwave cavities have been measured in the frequency range
below 20 GHz and analyzed using a statistical measure which is given by the
distribution of the normalized mode fluctuations. For chaotic systems the limit
distribution is conjectured to show a universal Gaussian, whereas integrable
systems should exhibit a non-Gaussian limit distribution. For the investigated
Bunimovich stadium and the 3D-Sinai billiard we find that the distribution is
in good agreement with this prediction. We study members of the family of
limacon billiards, having mixed dynamics. It turns out that in this case the
number of approximately 1000 eigenvalues for each billiard does not allow to
observe significant deviations from a Gaussian, whereas an also measured
circular billiard with regular dynamics shows the expected difference from a
Gaussian.Comment: 7 pages, RevTex, 5 postscript figure, to be published in Phys. Rev.
E. In case of any problems contact A. Baecker ([email protected]) or H.
Rehfeld ([email protected]
Experimental vs. Numerical Eigenvalues of a Bunimovich Stadium Billiard -- A Comparison
We compare the statistical properties of eigenvalue sequences for a gamma=1
Bunimovich stadium billiard. The eigenvalues have been obtained by two ways:
one set results from a measurement of the eigenfrequencies of a superconducting
microwave resonator (real system) and the other set is calculated numerically
(ideal system). The influence of the mechanical imperfections of the real
system in the analysis of the spectral fluctuations and in the length spectra
compared to the exact data of the ideal system are shown. We also discuss the
influence of a family of marginally stable orbits, the bouncing ball orbits, in
two microwave stadium billiards with different geometrical dimensions.Comment: RevTex, 8 pages, 8 figures (postscript), to be published in Phys.
Rev.
Wave Dynamical Chaos in a Superconducting Three-Dimensional Sinai Billiard
Based on very accurate measurements performed on a superconducting microwave
resonator shaped like a desymmetrized three-dimensional (3D) Sinai billiard, we
investigate for the first time spectral properties of the vectorial Helmholtz,
i.e. non-quantum wave equation for a classically totally chaotic and
theoretically precisely studied system. We are thereby able to generalize some
aspects of quantum chaos and present some results which are consequences of the
polarization features of the electromagnetic waves.Comment: 4 pages RevTex; 4 postscript figures; to be published in Phys. Rev.
Lett.; Info: [email protected]
Coupled Microwave Billiards as a Model for Symmetry Breaking
Two superconducting microwave billiards have been electromagnetically coupled
in a variable way. The spectrum of the entire system has been measured and the
spectral statistics analyzed as a function of the coupling strength. It is
shown that the results can be understood in terms of a random matrix model of
quantum mechanical symmetry breaking -- as e.g. the violation of parity or
isospin in nuclear physics.Comment: 4 pages, 5 figure
Magnetic transitions and magnetodielectric effect in the antiferromagnet SrNdFeO
We investigated the magnetic phase diagram of single crystals of
SrNdFeO by measuring the magnetic properties, the specific heat and the
dielectric permittivity. The system has two magnetically active ions, Fe
and Nd. The Fe spins are antiferromagnetically ordered below 360
K with the moments lying in the ab-plane, and undergo a reorientation
transition at about 35-37 K to an antiferromagnetic order with the moments
along the c-axis. A short-range, antiferromagnetic ordering of Nd along
the c-axis was attributed to the reorientation of Fe followed by a
long-range ordering at lower temperature [S. Oyama {\it et al.} J. Phys.:
Condens. Matter. {\bf 16}, 1823 (2004)]. At low temperatures and magnetic
fields above 8 T, the Nd moments are completely spin-polarized. The
dielectric permittivity also shows anomalies associated with spin configuration
changes, indicating that this compound has considerable coupling between spin
and lattice. A possible magnetic structure is proposed to explain the results.Comment: 8 pages, 10 figures, submitted to PR
A study of urban business centers with emphasis on retail string developments
Thesis (M.C.P.) Massachusetts Institute of Technology. Dept. of Architecture, 1954.Bibliography: leaves 127-130.by Leslie H. Graef.M.C.P
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