6,245,467 research outputs found
Variable-beamwidth antennas
Two effective designs have been developed for Cassegrain and Gregorian antenna configurations. Each provides for both high-gain and low-gain operations. Cassegrain system sacrifices some efficiency due to small amount of increased spillover loss. Gregorian system provides for independent spillover control with two feeds
Exchangeable Variable Models
A sequence of random variables is exchangeable if its joint distribution is
invariant under variable permutations. We introduce exchangeable variable
models (EVMs) as a novel class of probabilistic models whose basic building
blocks are partially exchangeable sequences, a generalization of exchangeable
sequences. We prove that a family of tractable EVMs is optimal under zero-one
loss for a large class of functions, including parity and threshold functions,
and strictly subsumes existing tractable independence-based model families.
Extensive experiments show that EVMs outperform state of the art classifiers
such as SVMs and probabilistic models which are solely based on independence
assumptions.Comment: ICML 201
Pressure variable capacitor
Fabrication of pressure-telemetry transducer
Variable Hardy Spaces
We develop the theory of variable exponent Hardy spaces. Analogous to the
classical theory, we give equivalent definitions in terms of maximal operators.
We also show that distributions in these spaces have an atomic decomposition
including a "finite" decomposition; this decomposition is more like the
decomposition for weighted Hardy spaces due to Stromberg and Torchinsky than
the classical atomic decomposition. As an application of the atomic
decomposition we show that singular integral operators are bounded on variable
Hardy spaces with minimal regularity assumptions on the exponent function
Variable-speed tail rotors for helicopters with variable-speed main rotors
Variable tail rotor speed is investigated as a method for reducing tail rotor power, and improving helicopter performance. A helicopter model able to predict the main rotor and tail rotor powers is presented, and the flight test data of the UH-60A helicopter is used for validation. The predictions of the main and tail rotor powers are generally in good agreement with flight tests, which justifies the use of the present method in analyzing main and tail rotors. Reducing the main rotor speed can result in lower main rotor power at certain flight conditions. However, it increases the main rotor torque and the corresponding required tail rotor thrust to trim, which then decreases the yaw control margin of the tail rotor. In hover, the tail rotor may not be able to provide enough thrust to counter the main rotor torque, if it is slowed to follow the main rotor speed. The main rotor speed corresponding to the minimum main rotor power increases, if the change of tail rotor power in hover is considered. As a helicopter translated to cruise, the induced power decreases, and the profile power increases, with the profile power dominating the tail rotor. Reducing the tail rotor speed in cruise reduces the profile power to give a 37% reduction in total tail rotor power and a 1.4% reduction to total helicopter power. In high speed flight, varying the tail rotor speed is ineffective for power reduction. The power reduction obtained by the variable tail rotor speed is reduced for increased helicopter weight
Locally optimal control of continuous variable entanglement
We consider a system of two bosonic modes each subject to the dynamics
induced by a thermal Markovian environment and we identify instantaneous, local
symplectic controls that minimise the loss of entanglement in the Gaussian
regime. By minimising the decrease of the logarithmic negativity at every
instant in time, it will be shown that a non-trivial, finite amount of local
squeezing helps to counter the effect of decoherence during the evolution. We
also determine optimal control routines in the more restrictive scenario where
the control operations are applied on only one of the two modes. We find that
applying an instantaneous control only at the beginning of the dynamics, i.e.
preparing an appropriate initial state, is the optimal strategy for states with
symmetric correlations and when the dynamics is the same on both modes. More
generally, even in asymmetric cases, the delayed decay of entanglement
resulting from the optimal preparation of the initial state with no further
action turns out to be always very close to the optimised control where
multiple operations are applied during the evolution. Our study extends
directly to mono-symmetric systems of any number of modes, i.e. to systems that
are invariant under any local permutation of the modes within any one
partition, as they are locally equivalent to two-mode systems.Comment: 10 pages, 6 figures, still no joke
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