8 research outputs found
Effect of trailing edge geometry and thickness on the performance of certain turbine stator blading
The experimental and analytical investigation included solid blades with five different trailing-edge thicknesses and four different trailing-edge geometries. One of the geometries was round, one was square, one was tapered from the suction surface, and the other tapered from the pressure surface. One of the trailing-edge thicknesses was sharp edged; the other four thicknesses were equivalent to about 5, 11, 16, and 20 percent of the blade throat width. The experimental results show increased efficiency loss for increased trailing-edge thickness for all trailing-edge geometries. The blade with round trailing edge, equal to about 11 percent of the blade throat width, had 60 percent more loss than the sharp-edged blade. For the same trailing-edge thickness, square trailing edges caused more loss than round trailing edges, and the tapered trailing edges caused about the same loss as the round trailing edges
New summing algorithm using ensemble computing
We propose an ensemble algorithm, which provides a new approach for
evaluating and summing up a set of function samples. The proposed algorithm is
not a quantum algorithm, insofar it does not involve quantum entanglement. The
query complexity of the algorithm depends only on the scaling of the
measurement sensitivity with the number of distinct spin sub-ensembles. From a
practical point of view, the proposed algorithm may result in an exponential
speedup, compared to known quantum and classical summing algorithms. However in
general, this advantage exists only if the total number of function samples is
below a threshold value which depends on the measurement sensitivity.Comment: 13 pages, 0 figures, VIth International Conference on Quantum
Communication, Measurement and Computing (Boston, 2002
Constant-time solution to the Global Optimization Problem using Bruschweiler's ensemble search algorithm
A constant-time solution of the continuous Global Optimization Problem (GOP)
is obtained by using an ensemble algorithm. We show that under certain
assumptions, the solution can be guaranteed by mapping the GOP onto a discrete
unsorted search problem, whereupon Bruschweiler's ensemble search algorithm is
applied. For adequate sensitivities of the measurement technique, the query
complexity of the ensemble search algorithm depends linearly on the size of the
function's domain. Advantages and limitations of an eventual NMR implementation
are discussed.Comment: 14 pages, 0 figure
Robust control of decoherence in realistic one-qubit quantum gates
We present an open loop (bang-bang) scheme to control decoherence in a
generic one-qubit quantum gate and implement it in a realistic simulation. The
system is consistently described within the spin-boson model, with interactions
accounting for both adiabatic and thermal decoherence. The external control is
included from the beginning in the Hamiltonian as an independent interaction
term. After tracing out the environment modes, reduced equations are obtained
for the two-level system in which the effects of both decoherence and external
control appear explicitly. The controls are determined exactly from the
condition to eliminate decoherence, i.e. to restore unitarity. Numerical
simulations show excellent performance and robustness of the proposed control
scheme.Comment: 21 pages, 8 figures, VIth International Conference on Quantum
Communication, Measurement and Computing (Boston, 2002
Targeting qubit states using open-loop control
We present an open-loop (bang-bang) scheme which drives an open two-level
quantum system to any target state, while maintaining quantum coherence
throughout the process. The control is illustrated by a realistic simulation
for both adiabatic and thermal decoherence. In the thermal decoherence regime,
the control achieved by the proposed scheme is qualitatively similar, at the
ensemble level, to the control realized by the quantum feedback scheme of Wang,
Wiseman, and Milburn [Phys. Rev. A 64, #063810 (2001)] for the spontaneous
emission of a two-level atom. The performance of the open-loop scheme compares
favorably against the quantum feedback scheme with respect to robustness,
target fidelity and transition times.Comment: 27 pages, 7 figure
Quantum risk-sensitive control
The purpose of this paper is to describe some recent results concerning optimal feedback control of quantum systems using risk-sensitive performance criteria. We employ quantum stochastic models to describe an important class of quantum systems and define a risk-sensitive criterion for these models. A suitable information state is introduced to solve the optimal control problem using dynamic programming. The results are illustrated by examples