446 research outputs found
Beyond the Heisenberg time: Semiclassical treatment of spectral correlations in chaotic systems with spin 1/2
The two-point correlation function of chaotic systems with spin 1/2 is
evaluated using periodic orbits. The spectral form factor for all times thus
becomes accessible. Equivalence with the predictions of random matrix theory
for the Gaussian symplectic ensemble is demonstrated. A duality between the
underlying generating functions of the orthogonal and symplectic symmetry
classes is semiclassically established
Rotating solitons and non-rotating, non-static black holes
It is shown that the non-Abelian black hole solutions have stationary
generalizations which are parameterized by their angular momentum and electric
Yang-Mills charge. In particular, there exists a non-static class of stationary
black holes with vanishing angular momentum. It is also argued that the
particle-like Bartnik-McKinnon solutions admit slowly rotating, globally
regular excitations. In agreement with the non-Abelian version of the staticity
theorem, these non-static soliton excitations carry electric charge, although
their non-rotating limit is neutral.Comment: 5 pages, REVTe
Universal spectral statistics in Wigner-Dyson, chiral and Andreev star graphs II: semiclassical approach
A semiclassical approach to the universal ergodic spectral statistics in
quantum star graphs is presented for all known ten symmetry classes of quantum
systems. The approach is based on periodic orbit theory, the exact
semiclassical trace formula for star graphs and on diagrammatic techniques. The
appropriate spectral form factors are calculated upto one order beyond the
diagonal and self-dual approximations. The results are in accordance with the
corresponding random-matrix theories which supports a properly generalized
Bohigas-Giannoni-Schmit conjecture.Comment: 15 Page
IEA annex 58 : full-scale empirical validation of detailed thermal simulation programs
As simulation programs become more widely used for building performance assessment and building regulations compliance, there is a need to ensure that there are good quality empirical datasets which can be used to assess the predictive accuracy of these programs. This paper summarises a detailed experiment carried out on two identical full-scale buildings located at the Fraunhofer IBP test site at Holzkirchen in Germany and the associated modelling of the buildings. The work was undertaken as part of IEA ECB Annex 58 "Reliable building energy performance characterization based on full scale dynamic measurements". The test sequence, applied to the side-by-side validation experiment conducted on the multi-roomed Twin Houses, consisted of periods of constant internal temperatures, a period of pseudo-random heat injections and a free-float period. All boundary and internal conditions were comprehensively monitored. Modelling teams were given details of the buildings and the boundary conditions, and over 20 teams submitted their predictions of the internal conditions which were subsequently compared with measurements. The paper focuses on a sensitivity study carried out to assess the overall prediction uncertainty resulting from the uncertainties in the input parameters, as well as identifying those inputs which had the most influence on predictions. An assessment of the measurement uncertainty is also included
Tunneling magnetoresistance in devices based on epitaxial NiMnSb with uniaxial anisotropy
We demonstrate tunnel magnetoresistance (TMR) junctions based on a tri layer
system consisting of an epitaxial NiMnSb, aluminum oxide and CoFe tri layer.
The junctions show a tunnelling magnetoresistance of Delta R/R of 8.7% at room
temperature which increases to 14.7% at 4.2K. The layers show clear separate
switching and a small ferromagnetic coupling. A uniaxial in plane anisotropy in
the NiMnSb layer leads to different switching characteristics depending on the
direction in which the magnetic field is applied, an effect which can be used
for sensor applications.Comment: 8 pages, 3 figures, submitted to Appl. Phys. Let
Can Dirac fermions Destroy Yang-Mills Black Hole?
We study the four-dimensional Einstein-Yang-Mills black hole in the presence
of Dirac fermion field. Assuming a spherically symmetric static asymptotically
flat black hole spacetime we consider both massless and massive fermion fields.
The (4+1)-dimensional Einstein-Yang-Mills system effectively reducing to
Einstein-Yang-Mills-Higgs-dilaton model, was also taken into account. One finds
that fermion vacuum leads to the destruction of black holes in question.Comment: 11 pages, RevTEx, to be published in Phys.Rev.D1
Periodic-Orbit Theory of Level Correlations
We present a semiclassical explanation of the so-called
Bohigas-Giannoni-Schmit conjecture which asserts universality of spectral
fluctuations in chaotic dynamics. We work with a generating function whose
semiclassical limit is determined by quadruplets of sets of periodic orbits.
The asymptotic expansions of both the non-oscillatory and the oscillatory part
of the universal spectral correlator are obtained. Borel summation of the
series reproduces the exact correlator of random-matrix theory.Comment: 4 pages, 1 figure (+ web-only appendix with 2 pages, 1 figure
Investigation of CoFeSi: The Heusler compound with Highest Curie Temperature and Magnetic Moment
This work reports on structural and magnetic investigations of the Heusler
compound CoFeSi. X-Ray diffraction and M\"o\ss bauer spectrometry indicate
an ordered structure. Magnetic measurements by means of X-ray magnetic
circular dichroism and magnetometry revealed that this compound is, currently,
the material with the highest magnetic moment () and Curie-temperature
(1100K) in the classes of Heusler compounds as well as half-metallic
ferromagnets
Half-metallic ferromagnetism with high magnetic moment and high Curie temperature in CoFeSi
CoFeSi crystallizes in the ordered L2 structure as proved by X-ray
diffraction and M\"o\ss bauer spectroscopy. The magnetic moment of CoFeSi
was measured to be about at 5K. Magnetic circular dichroism spectra
excited by soft X-rays (XMCD) were taken to determine the element specific
magnetic moments of Co and Fe. The Curie temperature was measured with
different methods to be ()K. CoFeSi was found to be the Heusler
compound as well as the half-metallic ferromagnet with the highest magnetic
moment and Curie temperature.Comment: conference contribution, MMM200
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