12,167 research outputs found
Psychophysical evidence for competition between real and illusory contour processing
Luminance defined and illusory contours provide vital information about object borders. However, real and illusory contour cues tend to be used under different contexts and can interfere with one another. Although some cells in visual cortex process both real and illusory contours equivalently, recent studies (Ramsden et al 2001) suggest competitive interactions between real (feedforward) and illusory (feedback) contour processing in primate V1 and V2. To test this hypothesis psychophysically, we designed stimuli in which illusory contours are presented with and without the presence of real line components. If real and illusory contour cues are processed by the same mechanism, then the presence of both cues should enhance the percept. If the illusory percept is degraded by the presence of real lines, then independent real and illusory mechanisms are suggested. The perception of a Kanisza-triangle, presented for 250 msec, was measured under three conditions: 1) virtual contour alone, 2) with a short parallel real line superimposed on the virtual contour or 3) with a short orthogonal real line abutting the virtual contour. The real lines were varied from sub- to supra-threshold contrasts. In a 2AFC paradigm three subjects fixated on a spot in the triangle center and indicated whether the side of the triangle was bent outwards or inwards. We found that real lines degraded the percept of the illusory contour (i.e. increased angular thresholds). Such interference occurred even at subthreshold real line contrasts and, in some subjects, was greater for the parallel than orthogonal real line. Our results support the presence of separate mechanisms for the processing of real and illusory contours and suggest that, under some circumstances, real cues can interfere with the processing of illusory cues. We suggest that such interferences occurs by the feedforward influences of the lines which interfere with the feedback influences prominent during illusory contour processing
Minimal kernels of Dirac operators along maps
Let be a closed spin manifold and let be a closed manifold. For maps
and Riemannian metrics on and on , we consider
the Dirac operator of the twisted Dirac bundle . To this Dirac operator one can associate an index
in . If is -dimensional, one gets a lower bound for
the dimension of the kernel of out of this index. We investigate
the question whether this lower bound is obtained for generic tupels
Including Systematic Uncertainties in Confidence Interval Construction for Poisson Statistics
One way to incorporate systematic uncertainties into the calculation of
confidence intervals is by integrating over probability density functions
parametrizing the uncertainties. In this note we present a development of this
method which takes into account uncertainties in the prediction of background
processes, uncertainties in the signal detection efficiency and background
efficiency and allows for a correlation between the signal and background
detection efficiencies. We implement this method with the Feldman & Cousins
unified approach with and without conditioning. We present studies of coverage
for the Feldman & Cousins and Neyman ordering schemes. In particular, we
present two different types of coverage tests for the case where systematic
uncertainties are included. To illustrate the method we show the relative
effect of including systematic uncertainties the case of dark matter search as
performed by modern neutrino tel escopes.Comment: 23 pages, 10 figures, replaced to match published versio
Land Use Conflict: When City and Country Clash
Urban sprawl is not a new phenomenon. Metropolitan areas have been growing and expanding for the past century, pushing development into rural areas. History has shown that rural-urban conflicts are often the result. During the second half of the twentieth century, the migration to the central city has been reversed, as people pour out of cities and into the suburbs. Today, increasingly complex rural-urban land use issues have continued to generate controversy
Acoustic Identification of Liquefaction Potential
The interparticle arrangement, or fabric, of sands is a key determinant of sample rigidity. This rigidity, in large part, determines the velocity and attenuation of acoustic transmissions in a test specimen, as well as its resistance to liquefaction. Utilizing high frequency small-amplitude compressional wave transmissions, different fabric arrangements of standard triaxial samples of the same sand have been reliably identified from their acoustic response. Both the compressional wave velocity and attenuation were used to determine the acoustic signature of a sample. Cyclic triaxial testing of the same laboratory-prepared samples revealed that there is direct relationship between the acoustic response of a sample prepared by a particular method and its resistance to liquefaction. The effect of stress history, induced by pre-shaking, on the resistance to liquefaction of a test sample was also detected by changes in the acoustic signature
A new 1.6-micron map of Titan’s surface
We present a new map of Titan's surface obtained in the spectral 'window' at ∼1.6 μm between strong methane absorption. This pre-Cassini view of Titan's surface was created from images obtained using adaptive optics on the W.M. Keck II telescope and is the highest resolution map yet made of Titan's surface. Numerous surface features down to the limits of the spatial resolution (∼200–300 km) are apparent. No features are easily identifiable in terms of their geologic origin, although several are likely craters
The Public Offering and a Quest for Alternatives
The year 1969 has seen a continuation of the strong new issues market that has commanded a significant portion of the attention of the investing public over the past few years. As a result, more and more closely held companies are seeking to raise funds through public offerings of their stock and thus share in the successes of this strong market. While the market conditions have been most encouraging,there have been other developments that have made the managements of some closely held companies reconsider the relative advantages and disadvantages of going public. Recent court decisions have strictly defined the legal responsibilities and potential liabilities of management of publicly held companies. The costs of going public, both in money and in the time of management, have also steadily increased. Moreover, these trends seem likely to continue as more extensive reporting requirements are applied to public companies under the federal securities laws. What is the real substance of these new cases and the costs of being a publicly held company? What is behind the furor over such cases as BarChris, Globus and Texas Gulf Sulphur? Are accountants,underwriters, lawyers, and corporate executives now required to meet impossible standards in the preparation of a registration statement and are they subject to substantial liabilities for any failure to fulfill these standards? Perhaps most importantly, how do these new developments affect the varied and interdependent questions and considerations against which a decision to go public has traditionally been measured? The purpose of this article is to answer some of these questions. It will analyze the advantages and disadvantages of going public in the context of these new cases and in the context of these increasing costs. It will then compare the results of going public with the results obtained by some other means of raising capital for closely held companies. From these analyses the reader can reach some conclusions as to the best course of action for his client or company to follow
Inference for bounded parameters
The estimation of signal frequency count in the presence of background noise
has had much discussion in the recent physics literature, and Mandelkern [1]
brings the central issues to the statistical community, leading in turn to
extensive discussion by statisticians. The primary focus however in [1] and the
accompanying discussion is on the construction of a confidence interval. We
argue that the likelihood function and -value function provide a
comprehensive presentation of the information available from the model and the
data. This is illustrated for Gaussian and Poisson models with lower bounds for
the mean parameter
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