2,369 research outputs found
Simulation of unsteady rotational flow over propfan configuration
During the past decade, aircraft engine manufacturers and scientists at NASA have worked on extending the high propulsive efficiency of a classical propeller to higher cruise Mach numbers. The resulting configurations use highly swept twisted and very thin blades to delay the drag divergence Mach number. Unfortunately, these blades are also susceptible to aeroelastic instabilities. This was observed for some advanced propeller configurations in wind tunnel tests at NASA Lewis Research Center, where the blades fluttered at cruise speeds. To address this problem and to understand the flow phenomena and the solid fluid interaction involved, a research effort was initiated at Georgia Institute of Technology in 1986, under the support of the Structural Dynamics Branch of the NASA Lewis Research Center. The objectives of this study are: (1) the development of solution procedures and computer codes capable of predicting the aeroelastic characteristics of modern single and counter-rotation propellers; and (2) the use of these solution procedures to understand physical phenomena such as stall flutter, transonic flutter, and divergence
Missing Shapiro steps and the -periodic Josephson effect in interacting helical electron systems
Two-particle backscattering in time-reversal invariant interacting helical
electron systems can lead to the formation of quasiparticles with charge .
We propose a way to detect such states by means of the Josephson effect in the
presence of proximity-induced superconductivity. In this case, the existence of
charges leads to an -periodic component of the Josephson current
which can be identified through measurement of Shapiro steps in Josephson
junctions. In particular, we show that even when there is weak explicit
time-reversal symmetry breaking, which causes the two-particle backscattering
to be a sub-leading effect at low energies, its presence can still be detected
in driven, current-biased Shapiro step measurements. The disappearance of some
of these steps as a function of the drive frequency is directly related to the
existence of non-Abelian zero-energy states. We suggest that this effect can be
measured in current state-of-the-art Rashba wires.Comment: 9 pages, 5 figures. A new submission extending and expanding our
analysis in arXiv:1507.08881. (v2) References adde
Dynamic response functions and helical gaps in interacting Rashba nanowires with and without magnetic fields
A partially gapped spectrum due to the application of a magnetic field is one
of the main probes of Rashba spin-orbit coupling in nanowires. Such a "helical
gap" manifests itself in the linear conductance, as well as in dynamic response
functions such as the spectral function, the structure factor, or the
tunnelling density of states. In this paper, we investigate theoretically the
signature of the helical gap in these observables with a particular focus on
the interplay between Rashba spin-orbit coupling and electron-electron
interactions. We show that in a quasi-one-dimensional wire, interactions can
open a helical gap even without magnetic field. We calculate the dynamic
response functions using bosonization, a renormalization group analysis, and
the exact form factors of the emerging sine-Gordon model. For special
interaction strengths, we verify our results by refermionization. We show how
the two types of helical gaps, caused by magnetic fields or interactions, can
be distinguished in experiments.Comment: 15 pages, 7 figures, v2 refs adde
Detecting nonlocal Cooper pair entanglement by optical Bell inequality violation
Based on the Bardeen Cooper Schrieffer (BCS) theory of superconductivity, the
coherent splitting of Cooper pairs from a superconductor to two spatially
separated quantum dots has been predicted to generate nonlocal pairs of
entangled electrons. In order to test this hypothesis, we propose a scheme to
transfer the spin state of a split Cooper pair onto the polarization state of a
pair of optical photons. We show that the produced photon pairs can be used to
violate a Bell inequality, unambiguously demonstrating the entanglement of the
split Cooper pairs.Comment: 11 pages, 9 figures, v3 with added reference
Recurrence Relations
The main aim of the paper is to obtain some recurrence relations for the generalized H-function of two variables
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