32,460 research outputs found
Dynamic response of two composite prop-fan models on a nacelle/wing/fuselage half model
Results are presented for blade response wind tunnel tests of two 62.2 cm diameter Prop-Fan (advanced turboprop) models with swept and unswept graphite/epoxy composite blades. Measurements of dynamic response were made with the rotors mounted on a simulated nacelle/wing/fuselage model, with varying tilt, at flow speeds up to 0.85 Mach number. The presence of the wing, downstream of the rotor, induced 1-P responses that were about twice those previously measured for an isolated nacelle installation. The swept blade had less 1-P response than the unswept (straight) blade. The 2-P response was significant for both blades, and was closely correlated to wing lift. Higher order response was not important for the straight blade, but possibly important for the swept blade near critical speeds, due to the proximity of the blade tips to the wing leading edge. Measurements are compared with theoretically based prediction. Correlations between calculated and measured 1-P response were good for the straight blade, and fair for the swept blade. Improvements to the calculation method were identified and implemented
Physical realizations of quantum operations
Quantum operations (QO) describe any state change allowed in quantum
mechanics, such as the evolution of an open system or the state change due to a
measurement. We address the problem of which unitary transformations and which
observables can be used to achieve a QO with generally different input and
output Hilbert spaces. We classify all unitary extensions of a QO, and give
explicit realizations in terms of free-evolution direct-sum dilations and
interacting tensor-product dilations. In terms of Hilbert space dimensionality
the free-evolution dilations minimize the physical resources needed to realize
the QO, and for this case we provide bounds for the dimension of the ancilla
space versus the rank of the QO. The interacting dilations, on the other hand,
correspond to the customary ancilla-system interaction realization, and for
these we derive a majorization relation which selects the allowed unitary
interactions between system and ancilla.Comment: 8 pages, no figures. Accepted for publication on Phys. Rev.
Compression and R-wave detection of ECG/VCG data
Application of information theory to eliminate redundant part of electrocardiogram or vectorcardiogram is described. Operation of medical equipment to obtain three dimensional study of patient is discussed. Use of fast Fourier transform to accomplish data compression is explained
Mixedness and teleportation
We show that on exceeding a certain degree of mixedness (as quantified by the
von Neumann entropy), entangled states become useless for teleporatation. By
increasing the dimension of the entangled systems, this entropy threshold can
be made arbitrarily close to maximal. This entropy is found to exceed the
entropy threshold sufficient to ensure the failure of dense coding.Comment: 6 pages, no figure
The Nature and Location of Quantum Information
Quantum information is defined by applying the concepts of ordinary (Shannon)
information theory to a quantum sample space consisting of a single framework
or consistent family. A classical analogy for a spin-half particle and other
arguments show that the infinite amount of information needed to specify a
precise vector in its Hilbert space is not a measure of the information carried
by a quantum entity with a -dimensional Hilbert space; the latter is,
instead, bounded by log d bits (1 bit per qubit). The two bits of information
transmitted in dense coding are located not in one but in the correlation
between two qubits, consistent with this bound. A quantum channel can be
thought of as a "structure" or collection of frameworks, and the physical
location of the information in the individual frameworks can be used to
identify the location of the channel. Analysis of a quantum circuit used as a
model of teleportation shows that the location of the channel depends upon
which structure is employed; for ordinary teleportation it is not (contrary to
Deutsch and Hayden) present in the two bits resulting from the Bell-basis
measurement, but in correlations of these with a distant qubit. In neither
teleportation nor dense coding does information travel backwards in time, nor
is it transmitted by nonlocal (superluminal) influences. It is (tentatively)
proposed that all aspects of quantum information can in principle be understood
in terms of the (basically classical) behavior of information in a particular
framework, along with the framework dependence of this information.Comment: Latex 29 pages, uses PSTricks for figure
Hexagonal as semiconducting ferroelectrics
We use a first-principles rational-design approach to identify a
previously-unrecognized class of ferroelectric materials in the LiGaGe
structure type. We calculate structural parameters, polarization and
ferroelectric well depths both for reported and as-yet hypothetical
representatives of this class. Our results provide guidance for the
experimental realization and further investigation of high-performance
materials suitable for practical applications.Comment: 5 pages, 2 figures, 3 table
Improving Quantum Query Complexity of Boolean Matrix Multiplication Using Graph Collision
The quantum query complexity of Boolean matrix multiplication is typically
studied as a function of the matrix dimension, n, as well as the number of 1s
in the output, \ell. We prove an upper bound of O (n\sqrt{\ell}) for all values
of \ell. This is an improvement over previous algorithms for all values of
\ell. On the other hand, we show that for any \eps < 1 and any \ell <= \eps
n^2, there is an \Omega(n\sqrt{\ell}) lower bound for this problem, showing
that our algorithm is essentially tight.
We first reduce Boolean matrix multiplication to several instances of graph
collision. We then provide an algorithm that takes advantage of the fact that
the underlying graph in all of our instances is very dense to find all graph
collisions efficiently
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