161,375 research outputs found
On the geometry of double field theory
Double field theory was developed by theoretical physicists as a way to
encompass -duality. In this paper, we express the basic notions of the
theory in differential-geometric invariant terms, in the framework of
para-Kaehler manifolds. We define metric algebroids, which are vector bundles
with a bracket of cross sections that has the same metric compatibility
property as a Courant bracket. We show that a double field gives rise to two
canonical connections, whose scalar curvatures can be integrated to obtain
actions. Finally, in analogy with Dirac structures, we define and study
para-Dirac structures on double manifolds.Comment: The paper will appear in J. Math. Phys., 201
Unconventional superconducting pairing symmetry induced by phonons
The possibility of non-s-wave superconductivity induced by phonons is
investigated using a simple model that is inspired by SrRuO. The model
assumes a two-dimensional electronic structure, a two-dimensional
spin-fluctuation spectrum, and three-dimensional electron-phonon coupling.
Taken separately, each interaction favors formation of spin-singlet pairs (of s
symmetry for the phonon interaction and d symmetry for the spin
interaction), but in combination, a variety of more unusual singlet and triplet
states are found, depending on the interaction parameters. This may have
important implications for SrRuO, providing a plausible explanation of
how the observed spin fluctuations, which clearly favor d pairing,
may still be instrumental in creating a superconducting state with a different
(e.g., p-wave) symmetry. It also suggests an interpretation of the large
isotope effect observed in SrRuO. These results indicate that phonons
could play a key role in establishing the order-parameter symmetry in
SrRuO, and possibly in other unconventional superconductors.Comment: 6 pages, 5 figures, submitted to Phys. Rev.
Isotropic subbundles of
We define integrable, big-isotropic structures on a manifold as
subbundles that are isotropic with respect to the
natural, neutral metric (pairing) of and are closed by
Courant brackets (this also implies that ). We give the interpretation of such a structure by objects of
, we discuss the local geometry of the structure and we give a reduction
theorem.Comment: LaTex, 37 pages, minimization of the defining condition
Decoherence of coupled electron spins via nuclear spin dynamics in quantum dots
In double quantum dots, the exchange interaction between two electron spins
renormalizes the excitation energy of pair-flips in the nuclear spin bath,
which in turn modifies the non-Markovian bath dynamics. As the energy
renormalization varies with the Overhauser field mismatch between the quantum
dots, the electron singlet-triplet decoherence resulting from the bath dynamics
depends on sampling of nuclear spin states from an ensemble, leading to the
transition from exponential decoherence in single-sample dynamics to power-law
decay under ensemble averaging. In contrast, the decoherence of a single
electron spin in one dot is essentially the same for different choices of the
nuclear spin configuration.Comment: 4 pages 3 figure
Parallel detrended fluctuation analysis for fast event detection on massive PMU data
("(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.")Phasor measurement units (PMUs) are being rapidly deployed in power grids due to their high sampling rates and synchronized measurements. The devices high data reporting rates present major computational challenges in the requirement to process potentially massive volumes of data, in addition to new issues surrounding data storage. Fast algorithms capable of processing massive volumes of data are now required in the field of power systems. This paper presents a novel parallel detrended fluctuation analysis (PDFA) approach for fast event detection on massive volumes of PMU data, taking advantage of a cluster computing platform. The PDFA algorithm is evaluated using data from installed PMUs on the transmission system of Great Britain from the aspects of speedup, scalability, and accuracy. The speedup of the PDFA in computation is initially analyzed through Amdahl's Law. A revision to the law is then proposed, suggesting enhancements to its capability to analyze the performance gain in computation when parallelizing data intensive applications in a cluster computing environment
Electron Density Dependence of in-plane Spin Relaxation Anisotropy in GaAs/AlGaAs Two-Dimensional Electron Gas
We investigated the spin dynamics of two-dimensional electrons in (001)
GaAs/AlGaAs heterostructure using the time resolved Kerr rotation technique
under a transverse magnetic field. The in-plane spin lifetime is found to be
anisotropic below 150k due to the interference of Rashba and Dresselhaus
spin-orbit coupling and D'yakonov-Perel' spin relaxation. The ratio of in-plane
spin lifetimes is measured directly as a function of temperature and pump
power, showing that the electron density in 2DEG channel strongly affects the
Rashba spin-orbit coupling.Comment: 3 pages, 2 figure
Parallel detrended fluctuation analysis for fast event detection on massive PMU data
("(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.")Phasor measurement units (PMUs) are being rapidly deployed in power grids due to their high sampling rates and synchronized measurements. The devices high data reporting rates present major computational challenges in the requirement to process potentially massive volumes of data, in addition to new issues surrounding data storage. Fast algorithms capable of processing massive volumes of data are now required in the field of power systems. This paper presents a novel parallel detrended fluctuation analysis (PDFA) approach for fast event detection on massive volumes of PMU data, taking advantage of a cluster computing platform. The PDFA algorithm is evaluated using data from installed PMUs on the transmission system of Great Britain from the aspects of speedup, scalability, and accuracy. The speedup of the PDFA in computation is initially analyzed through Amdahl's Law. A revision to the law is then proposed, suggesting enhancements to its capability to analyze the performance gain in computation when parallelizing data intensive applications in a cluster computing environment
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