28,196 research outputs found
Hierarchical stack filtering : a bitplane-based algorithm for massively parallel processors
With the development of novel parallel architectures for image processing, the implementation
of well-known image operators needs to be reformulated to take advantage of the so-called
massive parallelism. In this work, we propose a general algorithm that implements a large
class of nonlinear filters, called stack filters, with a 2D-array processor. The proposed method consists of decomposing an image into bitplanes with the bitwise decomposition, and then process every bitplane hierarchically. The filtered image is reconstructed by simply stacking the filtered bitplanes according to their order of significance. Owing to its hierarchical structure, our algorithm allows us to trade-off between image quality and processing time, and to significantly reduce the computation time of low-entropy images. Also, experimental tests show that the processing time of our method is substantially lower than that of classical methods when using large structuring elements. All these features are of interest to a variety of real-time applications based on morphological operations such as video segmentation and video enhancement
Photophoretic Structuring of Circumstellar Dust Disks
We study dust accumulation by photophoresis in optically thin gas disks.
Using formulae of the photophoretic force that are applicable for the free
molecular regime and for the slip-flow regime, we calculate dust accumulation
distances as a function of the particle size. It is found that photophoresis
pushes particles (smaller than 10 cm) outward. For a Sun-like star, these
particles are transported to 0.1-100 AU, depending on the particle size, and
forms an inner disk. Radiation pressure pushes out small particles (< 1 mm)
further and forms an extended outer disk. Consequently, an inner hole opens
inside ~0.1 AU. The radius of the inner hole is determined by the condition
that the mean free path of the gas molecules equals the maximum size of the
particles that photophoresis effectively works on (100 micron - 10 cm,
depending on the dust property). The dust disk structure formed by
photophoresis can be distinguished from the structure of gas-free dust disk
models, because the particle sizes of the outer disks are larger, and the inner
hole radius depends on the gas density.Comment: 15 pages, 9 figures, Accepted by ApJ; corrected a typo in the author
nam
Digital implementation of the cellular sensor-computers
Two different kinds of cellular sensor-processor architectures are used nowadays in various
applications. The first is the traditional sensor-processor architecture, where the sensor and the
processor arrays are mapped into each other. The second is the foveal architecture, in which a
small active fovea is navigating in a large sensor array. This second architecture is introduced
and compared here. Both of these architectures can be implemented with analog and digital
processor arrays. The efficiency of the different implementation types, depending on the used
CMOS technology, is analyzed. It turned out, that the finer the technology is, the better to use
digital implementation rather than analog
Design of ultraprecision machine tools with application to manufacturing of miniature and micro components
Currently the underlying necessities for predictability, producibility and productivity remain big issues in ultraprecision machining of miniature/microproducts. The demand on rapid and economic fabrication of miniature/microproducts with complex shapes has also made new challenges for ultraprecision machine tool design. In this paper the design for an ultraprecision machine tool is introduced by describing its key machine elements and machine tool design procedures. The focus is on the review and assessment of the state-of-the-art ultraprecision machining tools. It also illustrates the application promise of miniature/microproducts. The trends on machine tool development, tooling, workpiece material and machining processes are pointed out
Nanoscale precision of 3D polymerisation via polarisation control
A systematic analysis of polarization effects in a direct write femtosecond
laser 3D lithography is presented. It is newly shown that coupling between
linear polarization of the writing light electric field and temperature
gradient can be used to fine-tune feature sizes in structuring of photoresists
at a nanoscale. The vectorial Debye focusing is used to simulate polarization
effects and a controlled variation up to 20% in the linewidth is shown
experimentally for the identical axial extent of the polymerised features. The
revealed mechanisms are relevant for a wide range of phenomena of light-matter
interaction at tight focusing in laser-tweezers and in plasmonic or dielectric
sub-wavelength focusing where strong light intensity and thermal gradients
coexist.Comment: 15 pages, 3 figure
Light driven structuring of glasses
Theoretical and experimental evidence of light driven structuring of glasses
is presented. We show that light overcomes Coulomb repulsion and effective
electron-electron interaction in glasses under strong light pumping becomes
attractive. As the result homogenious distribution of trapped electrons gets
unstable and macroscopic electron bunches are grown. At different conditions
ordered structures with period about 2 microns determined by internal
properties of the material are formed These structures were observed in
ablation: surface profile after laser treatment reveals ordered pattern
corresponding to the light induced electron domains.Comment: 7 pages, 6 figure
Theory of fishnet negative-index optical metamaterials
We theoretically study fishnet metamaterials at optical frequencies. In
contrast to earlier works, we provide a microscopic description by tracking the
transversal and longitudinal flows of energy through the fishnet mesh composed
of intersecting subwavelength plasmonic waveguides. The analysis is supported
by a semi-analytical model based on surface-plasmon coupled-mode equations,
which provides accurate formulas for the fishnet refractive index, including
the real-negative and imaginary parts. The model simply explains how the
surface plasmons couple at the waveguide intersections and it shines new light
on the fishnet negative-index paradigm at optical frequencies. Extension of the
theory for loss-compensated metamaterials with gain media is also presented.Comment: 4 figure
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