787 research outputs found
Optical orthogonal codes obtained from conics on finite projective planes
AbstractOptical orthogonal codes can be applied to fiber optical code division multiple access (CDMA) communications. In this paper, we show that optical orthogonal codes with auto- and cross-correlations at most 2 can be obtained from conics on a finite projective plane. In addition, the obtained codes asymptotically attain the upper bound on the number of codewords when the order q of the base field is large enough
Tracking the apparent location of targets in interpolated motion
AbstractUnder appropriate conditions, a target moving in discrete steps can appear to move smoothly and continuously even within the portions of the path where no physical stimulus is present. We investigated the nature of this interpolated motion in attentive tracking displays as well as apparent motion. The results showed that the apparent location of the target moved smoothly through space between the two discrete locations and the judgements of interpolated motion for attentive tracking and apparent motion were comparable to those for continuous motion in both the perceived path and the precision of the judgements. There were few, if any, differences between judgements for real and interpolated motion. An alignment procedure showed that the smooth change in location judgements was real and not a consequence of averaging across discrete locations actually seen on each trial. We also found that the slowest alternation rate which supported accurate location judgements corresponded to a critical SOA of about 500 ms, similar to the longest SOA which supported a subjective impression of motion in the display. Deviations from a constant velocity which were shorter than 200 ms did not register in the judged motion path, suggesting a fairly long time constant for the integration of velocity information into the perceived motion. These results suggest a specialized motion analysis which provides an accurate, explicit model of the interpolated motion path
Desingularization of matrix equations employing hypersingular integrals in boundary element methods using double nodes
In boundary element methods, the method of using double nodes at corners is a
useful approach to uniquely define the normal direction of boundary elements.
However, matrix equations constructed by conventional boundary integral
equations (CBIE) become singular under certain combinations of double node
boundary conditions. In this paper, we analyze the singular conditions of the
CBIE formulation for cases where the boundary conditions at the double node are
imposed by combinations of Dirichlet, Neumann, Robin, and interface conditions.
To address this singularity we propose the use of hypersingular integral
equations (HBIE) for wave propagation problems that obey Helmholtz equation. To
demonstrate the applicability of HBIE, we compare three types of simultaneous
equations: (i) CBIE, (ii) partial-HBIE in which HBIE is only applied to the
double nodes at corners while CBIE is applied to the other nodes, and (iii)
full-HBIE in which HBIE is applied to all nodes. Based on our numerical
results, we observe the following results. The singularity of the matrix
equations for problems with any combination of boundary conditions can be
resolved by both full-HBIE and partial-HBIE, and partial-HBIE exhibits better
accuracy than full-HBIE. Furthermore, the computational cost of partial-HBIE is
smaller than that of full-HBIE.Comment: 14 pages, 10 figures, accepted manuscript submitted to Engineering
Analysis with Boundary Elemen
Wavefront restoration from lateral shearing data using spectral interpolation
Although a lateral-shear interferometer is robust against optical component
vibrations, its interferogram provides information about differential
wavefronts rather than the wavefronts themselves, resulting in the loss of
specific frequency components. Previous studies have addressed this limitation
by measuring four interferograms with different shear amounts to accurately
restore the two-dimensional wavefront. This study proposes a technique that
employs spectral interpolation to reduce the number of required interferograms.
The proposed approach introduces an origin-shift technique for accurate
spectral interpolation, which in turn is implemented by combining two methods:
natural extension and least-squares determination of ambiguities in uniform
biases. Numerical simulations confirmed that the proposed method accurately
restored a two-dimensional wavefront from just two interferograms, thereby
indicating its potential to address the limitations of the lateral-shear
interferometer.Comment: 11 pages, 6 figure
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