1,617 research outputs found
Improvement of Surface Accuracy and Shop Floor Feed Rate Smoothing Through Open CNC Monitoring System and Cutting Simulation
AbstractIn the milling process of complex workpiece shapes the feed rate normally becomes instable due to the high degree of surface curvature that requires high acceleration and deceleration of the interpolated axes. This condition impacts on process time and on the surface accuracy regarding the manufactured part form and texture. The challenge to simulate the real machine and control behavior requires accurate models with a set of experiments to tune and dimension the model to the respective machine tool. The aim is to improve the HSC milling process of complex surfaces before removing any material. In this paper experiments show that the surface form accuracy and texture can be optimized through an automatic feed rate smoothing of the finishing operation directly on the machine tool. The axis positions and spindle speeds monitored through the open CNC are used as input for a geometric cutting simulation, thus enabling to predict and optimize the surface quality
Thermoacoustic tomography arising in brain imaging
We study the mathematical model of thermoacoustic and photoacoustic
tomography when the sound speed has a jump across a smooth surface. This models
the change of the sound speed in the skull when trying to image the human
brain. We derive an explicit inversion formula in the form of a convergent
Neumann series under the assumptions that all singularities from the support of
the source reach the boundary
Uhlmann's geometric phase in presence of isotropic decoherence
Uhlmann's mixed state geometric phase [Rep. Math. Phys. {\bf 24}, 229 (1986)]
is analyzed in the case of a qubit affected by isotropic decoherence treated in
the Markovian approximation. It is demonstrated that this phase decreases
rapidly with increasing decoherence rate and that it is most fragile to weak
decoherence for pure or nearly pure initial states. In the unitary case, we
compare Uhlmann's geometric phase for mixed states with that occurring in
standard Mach-Zehnder interferometry [Phys. Rev. Lett. {\bf 85}, 2845 (2000)]
and show that the latter is more robust to reduction in the length of the Bloch
vector. We also describe how Uhlmann's geometric phase in the present case
could in principle be realized experimentally.Comment: New ref added, refs updated, journal ref adde
Geometric phases for non-degenerate and degenerate mixed states
This paper focuses on the geometric phase of general mixed states under
unitary evolution. Here we analyze both non-degenerate as well as degenerate
states. Starting with the non-degenerate case, we show that the usual procedure
of subtracting the dynamical phase from the total phase to yield the geometric
phase for pure states, does not hold for mixed states. To this end, we furnish
an expression for the geometric phase that is gauge invariant. The parallelity
conditions are shown to be easily derivable from this expression. We also
extend our formalism to states that exhibit degeneracies. Here with the
holonomy taking on a non-abelian character, we provide an expression for the
geometric phase that is manifestly gauge invariant. As in the case of the
non-degenerate case, the form also displays the parallelity conditions clearly.
Finally, we furnish explicit examples of the geometric phases for both the
non-degenerate as well as degenerate mixed states.Comment: 23 page
Neural Adaptive Control of a Robot Joint Using Secondary Encoders
Using industrial robots for machining applications in flexible manufacturing
processes lacks a high accuracy. The main reason for the deviation is the
flexibility of the gearbox. Secondary Encoders (SE) as an additional, high precision
angle sensor offer a huge potential of detecting gearbox deviations. This paper
aims to use SE to reduce gearbox compliances with a feed forward, adaptive
neural control. The control network is trained with a second network for system
identification. The presented algorithm is capable of online application and optimizes
the robot accuracy in a nonlinear simulation
Distribuição vertical de oito espécies epifíticas na Floresta Ombrófila Densa em Santa Catarina.
Geometric observation for the Bures fidelity between two states of a qubit
In this Brief Report, we present a geometric observation for the Bures
fidelity between two states of a qubit.Comment: 4 pages, 1 figure, RevTex, Accepted by Phys. Rev.
Locating Overlap Information in Quantum Systems
When discussing the black hole information problem the term ``information
flow'' is frequently used in a rather loose fashion. In this article I attempt
to make this notion more concrete. I consider a Hilbert space which is
constructed as a tensor product of two subspaces (representing for example
inside and outside the black hole). I discuss how the system has the capacity
to contain information which is in NEITHER of the subspaces. I attempt to
quantify the amount of information located in each of the two subspaces, and
elsewhere, and analyze the extent to which unitary evolution can correspond to
``information flow''. I define the notion of ``overlap information'' which
appears to be well suited to the problem.Comment: 25 pages plain LaTeX, no figures. Imperial/TP/93-94/2
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