6,566 research outputs found
Long-term temporal dependence of droplets transiting through a fixed spatial point in gas-liquid twophase turbulent jets
We perform rescaled range analysis upon the signals measured by Dual Particle
Dynamical Analyzer in gas-liquid two-phase turbulent jets. A novel rescaled
range analysis is proposed to investigate these unevenly sampled signals. The
Hurst exponents of velocity and other passive scalars in the bulk of spray are
obtained to be 0.590.02 and the fractal dimension is hence 1.41
0.02, which are in remarkable agreement with and much more precise than
previous results. These scaling exponents are found to be independent of the
configuration and dimensions of the nozzle and the fluid flows. Therefore, such
type of systems form a universality class with invariant scaling properties.Comment: 16 Elsart pages including 8 eps figure
Continuous quantum feedback of coherent oscillations in a solid-state qubit
We have analyzed theoretically the operation of the Bayesian quantum feedback
of a solid-state qubit, designed to maintain perfect coherent oscillations in
the qubit for arbitrarily long time. In particular, we have studied the
feedback efficiency in presence of dephasing environment and detector
nonideality. Also, we have analyzed the effect of qubit parameter deviations
and studied the quantum feedback control of an energy-asymmetric qubit.Comment: 11 page
Measurements of the instantaneous velocity difference and local velocity with a fiber-optic coupler
New optical arrangements with two single-mode input fibers and a fiber-optic
coupler are devised to measure the instantaneous velocity difference and local
velocity. The fibers and the coupler are polarization-preserving to guarantee a
high signal-to-noise ratio. When the two input fibers are used to collect the
scattered light with the same momentum transfer vector but from two spatially
separated regions in a flow, the obtained signals interfere when combined via
the fiber-optic coupler. The resultant light received by a photomultiplier tube
contains a cross-beat frequency proportional to the velocity difference between
the two measuring points. If the two input fibers are used to collect the
scattered light from a common scattering region but with two different momentum
transfer vectors, the resultant light then contains a self-beat frequency
proportional to the local velocity at the measuring point. The experiment shows
that both the cross-beat and self-beat signals are large and the standard laser
Doppler signal processor can be used to measure the velocity difference and
local velocity in real time. The new technique will have various applications
in the general area of fluid dynamics.Comment: Patent number: 67437 for associated information on the hardware, see
http://karman.phyast.pitt.edu/horvath
Demonstration of Universal Parametric Entangling Gates on a Multi-Qubit Lattice
We show that parametric coupling techniques can be used to generate selective
entangling interactions for multi-qubit processors. By inducing coherent
population exchange between adjacent qubits under frequency modulation, we
implement a universal gateset for a linear array of four superconducting
qubits. An average process fidelity of is estimated for
three two-qubit gates via quantum process tomography. We establish the
suitability of these techniques for computation by preparing a four-qubit
maximally entangled state and comparing the estimated state fidelity against
the expected performance of the individual entangling gates. In addition, we
prepare an eight-qubit register in all possible bitstring permutations and
monitor the fidelity of a two-qubit gate across one pair of these qubits.
Across all such permutations, an average fidelity of
is observed. These results thus offer a path to a scalable architecture with
high selectivity and low crosstalk
(1+1)-dimensional turbulence
A class of dynamical models of turbulence living on a one-dimensional
dyadic-tree structure is introduced and studied. The models are obtained as a
natural generalization of the popular GOY shell model of turbulence. These
models are found to be chaotic and intermittent. They represent the first
example of (1+1)-dimensional dynamical systems possessing non trivial
multifractal properties. The dyadic structure allows to study spatial and
temporal fluctuations. Energy dissipation statistics and its scaling properties
are studied. Refined Kolmogorov Hypothesis is found to hold.Comment: 18 pages, 9 figures, submitted to Phys.of Fluid
Experimental Implementation of the Quantum Baker's Map
This paper reports on the experimental implementation of the quantum baker's
map via a three bit nuclear magnetic resonance (NMR) quantum information
processor. The experiments tested the sensitivity of the quantum chaotic map to
perturbations. In the first experiment, the map was iterated forward and then
backwards to provide benchmarks for intrinsic errors and decoherence. In the
second set of experiments, the least significant qubit was perturbed in between
the iterations to test the sensitivity of the quantum chaotic map to applied
perturbations. These experiments are used to investigate previous predicted
properties of quantum chaotic dynamics.Comment: submitted to PR
Trends in reliability modeling technology for fault tolerant systems
Reliability modeling for fault tolerant avionic computing systems was developed. The modeling of large systems involving issues of state size and complexity, fault coverage, and practical computation was discussed. A novel technique which provides the tool for studying the reliability of systems with nonconstant failure rates is presented. The fault latency which may provide a method of obtaining vital latent fault data is measured
A hybrid MPI-OpenMP scheme for scalable parallel pseudospectral computations for fluid turbulence
A hybrid scheme that utilizes MPI for distributed memory parallelism and
OpenMP for shared memory parallelism is presented. The work is motivated by the
desire to achieve exceptionally high Reynolds numbers in pseudospectral
computations of fluid turbulence on emerging petascale, high core-count,
massively parallel processing systems. The hybrid implementation derives from
and augments a well-tested scalable MPI-parallelized pseudospectral code. The
hybrid paradigm leads to a new picture for the domain decomposition of the
pseudospectral grids, which is helpful in understanding, among other things,
the 3D transpose of the global data that is necessary for the parallel fast
Fourier transforms that are the central component of the numerical
discretizations. Details of the hybrid implementation are provided, and
performance tests illustrate the utility of the method. It is shown that the
hybrid scheme achieves near ideal scalability up to ~20000 compute cores with a
maximum mean efficiency of 83%. Data are presented that demonstrate how to
choose the optimal number of MPI processes and OpenMP threads in order to
optimize code performance on two different platforms.Comment: Submitted to Parallel Computin
- …