526 research outputs found
Chirp filtering in the fractional Fourier Domain
Cataloged from PDF version of article.In the Wigner domain of a one-dimensional function, a certain chirp term represents a rotated line delta
function. On the other hand, a fractional Fourier transform (FRT) can be associated with a rotation of
the Wigner-distribution function by an angle connected with the FRT order. Thus with the FRT tool a chirp and a delta function can be transformed one into the other. Taking the chirp as additive noise, the
FRT is used for filtering the line delta function in the appropriate fractional Fourier domain.
Experimental filtering results for a Gaussian input function, which is modulated by an additive chirp noise, are shown. Excellent agreement between experiments and computer simulations is achieved
Fractional Fourier Transform- Simulations and experimental results
Cataloged from PDF version of article.Recently two optical interpretations of the fractional Fourier transform operator were introduced. We
address implementation issues of the fractional-Fourier-transform operation. We show that the original
bulk-optics configuration for performing the fractional-Fourier-transform operation 3J. Opt. Soc. Am. A
10, 2181 1199324 provides a scaled output using a fixed lens. For obtaining a non-scaled output, an
asymmetrical setup is suggested and tested. For comparison, computer simulations were performed.
A good agreement between computer simulations and experimental results was obtained
Anamorphic Fractional Fourier Transforming--Optical Implementation and Applications
Cataloged from PDF version of article.An additional degree of freedom is introduced to fractional-Fourier-transform systems by use of anamorphic optics. A different fractional Fourier order along the orthogonal principal directions is performed. A laboratory experimental system shows preliminary results that demonstrate the proposed theory. Applications such as anamorphic fractional correlation and multiplexing in fractional domains are briefly suggested. (C) 1995 Optical Society of Americ
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Electrophysiological Evidence of Attentional Biases in Social Anxiety Disorder
Background: Previous studies investigating attentional biases in social anxiety disorder (SAD) have yielded mixed results. Recent event-related potential (ERP) studies using the dot-probe paradigm in non-anxious participants have shown that the P1 component is sensitive to visuospatial attention towards emotional faces. We used a dot-probe task in conjunction with high-density ERPs and source localization to investigate attentional biases in SAD.
Method: Twelve SAD and 15 control participants performed a modified dot-probe task using angry–neutral and happy–neutral face pairs. The P1 component elicited by face pairs was analyzed to test the hypothesis that SAD participants would display early hypervigilance to threat-related cues. The P1 component to probes replacing angry, happy or neutral faces was used to evaluate whether SAD participants show either sustained hypervigilance or decreased visual processing of threat-related cues at later processing stages.
Results: Compared to controls, SAD participants showed relatively (a) potentiated P1 amplitudes and fusiform gyrus (FG) activation to angry–neutral versus happy–neutral face pairs; (b) decreased P1 amplitudes to probes replacing emotional (angry and happy) versus neutral faces; and (c) higher sensitivity (d′) to probes following angry–neutral versus happy–neutral face pairs. SAD participants also showed significantly shorter reaction times (RTs) to probes replacing angry versus happy faces, but no group differences emerged for RT.
Conclusions: The results provide electrophysiological support for early hypervigilance to angry faces in SAD with involvement of the FG, and reduced visual processing of emotionally salient locations at later stages of information processing, which might be a manifestation of attentional avoidance.Psycholog
A computational analysis of lower bounds for big bucket production planning problems
In this paper, we analyze a variety of approaches to obtain lower bounds for multi-level production planning problems with big bucket capacities, i.e., problems in which multiple items compete for the same resources. We give an extensive survey of both known and new methods, and also establish relationships between some of these methods that, to our knowledge, have not been presented before. As will be highlighted, understanding the substructures of difficult problems provide crucial insights on why these problems are hard to solve, and this is addressed by a thorough analysis in the paper. We conclude with computational results on a variety of widely used test sets, and a discussion of future research
The Top-Dog Index: A New Measurement for the Demand Consistency of the Size Distribution in Pre-Pack Orders for a Fashion Discounter with Many Small Branches
We propose the new Top-Dog-Index, a measure for the branch-dependent historic
deviation of the supply data of apparel sizes from the sales data of a fashion
discounter. A common approach is to estimate demand for sizes directly from the
sales data. This approach may yield information for the demand for sizes if
aggregated over all branches and products. However, as we will show in a
real-world business case, this direct approach is in general not capable to
provide information about each branch's individual demand for sizes: the supply
per branch is so small that either the number of sales is statistically too
small for a good estimate (early measurement) or there will be too much
unsatisfied demand neglected in the sales data (late measurement). Moreover, in
our real-world data we could not verify any of the demand distribution
assumptions suggested in the literature. Our approach cannot estimate the
demand for sizes directly. It can, however, individually measure for each
branch the scarcest and the amplest sizes, aggregated over all products. This
measurement can iteratively be used to adapt the size distributions in the
pre-pack orders for the future. A real-world blind study shows the potential of
this distribution free heuristic optimization approach: The gross yield
measured in percent of gross value was almost one percentage point higher in
the test-group branches than in the control-group branches.Comment: 22 pages, 15 figure
The Nuclear Bulge of the Galaxy. III. Large-Scale Physical Characteristics of Stars and Interstellar Matter
We analyse IRAS and COBE DIRBE data at wavelengths between 2.2 and 240 mu of
the central 500pc of the Galaxy and derive the large-scale distribution of
stars and interstellar matter in the Nuclear Bulge. Models of the Galactic Disk
and Bulge are developed in order to correctly decompose the total surface
brightness maps and to apply proper extinction corrections. The Nuclear Bulge
appears as a distinct, massive disk-like complex of stars and molecular clouds
which is, on a large scale, symmetric with respect to the Galactic Centre. It
is distinguished from the Galactic Bulge by its flat disk-like morphology, very
high density of stars and molecular gas, and ongoing star formation. The
Nuclear Bulge consists of an R^-2 Nuclear Stellar Cluster at the centre, a
large Nuclear Stellar Disk with radius 230+-20 pc and scale height 45+-5 pc,
and a Nuclear Molecular Disk of same size. Its total stellar mass and
luminosity are 1.4+-0.6 10^9 M_sun and 2.5+-1 10^9 L_sun, respectively. The
total mass of interstellar hydrogen in the Nuclear Bulge is 2+-0.3 10^7 M_sun.
Interstellar matter in the Nuclear Bulge is very clumpy with ~90% of the mass
contained in dense and massive molecular clouds with a volume filling factor of
only a few per cent. This extreme clumpiness enables the strong interstellar
radiation field to penetrate the entire Nuclear Bulge and explains the
relatively low average extinction towards the Galactic Centre. In addition, we
find 4 10^7 M_sun of cold and dense material located outside the Nuclear Bulge,
which gives rise to the observed asymmetry in the distribution of interstellar
matter in the Central Molecular Zone.Comment: 28 pages, 22 figures, accepted for publication in A&
Spectral imaging of the Central Molecular Zone in multiple 3-mm molecular lines
We have mapped 20 molecular lines in the Central Molecular Zone (CMZ) around
the Galactic Centre, emitting from 85.3 to 93.3 GHz. This work used the 22-m
Mopra radio telescope in Australia, equipped with the 8-GHz bandwidth UNSW-MOPS
digital filter bank, obtaining \sim 2 km/s spectral and \sim 40 arcsec spatial
resolution. The lines measured include emission from the c-C3H2, CH3CCH, HOCO+,
SO, H13CN, H13CO+, SO, H13NC, C2H, HNCO, HCN, HCO+, HNC, HC3N, 13CS and N2H+
molecules. The area covered is Galactic longitude -0.7 to 1.8 deg. and latitude
-0.3 to 0.2 deg., including the bright dust cores around Sgr A, Sgr B2, Sgr C
and G1.6-0.025. We present images from this study and conduct a principal
component analysis on the integrated emission from the brightest 8 lines. This
is dominated by the first component, showing that the large-scale distribution
of all molecules are very similar. We examine the line ratios and optical
depths in selected apertures around the bright dust cores, as well as for the
complete mapped region of the CMZ. We highlight the behaviour of the bright
HCN, HNC and HCO+ line emission, together with that from the 13C isotopologues
of these species, and compare the behaviour with that found in extra-galactic
sources where the emission is unresolved spatially. We also find that the
isotopologue line ratios (e.g. HCO+/H13CO+) rise significantly with increasing
red-shifted velocity in some locations. Line luminosities are also calculated
and compared to that of CO, as well as to line luminosities determined for
external galaxies.Comment: 27 pages, 15 figures, 12 tables, accepted by MNRA
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