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QuestPlus: A MATLAB Implementation of the QUEST+ adaptive Psychometric Method
QuestPlus is a MATLAB implementation of the QUEST+ adaptive psychometric method. It provides a rapid and flexible method of estimating the parameters of a psychophysical model, and is also capable of advising the user on the most appropriate stimuli to present, and on when to terminate testing. Of particular note is the algorithm’s ability to use prior information, its ability to determine the maximally informative stimulus on each trial, its ability to fit arbitrarily complex models, and its ability to vary multiple stimulus properties simultaneously
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A tutorial on cue combination and Signal Detection Theory: Using changes in sensitivity to evaluate how observers integrate sensory information
Many sensory inputs contain multiple sources of information (‘cues’), such as two sounds of different frequencies, or a voice heard in unison with moving lips. Often, each cue provides a separate estimate of the same physical attribute, such as the size or location of an object. An ideal observer can exploit such redundant sensory information to improve the accuracy of their perceptual judgments. For example, if each cue is modeled as an independent, Gaussian, random variable, then combining Ncues should provide up to a √N improvement in detection/discrimination sensitivity. Alternatively, a less efficient observer may base their decision on only a subset of the available information, and so gain little or no benefit from having access to multiple sources of information. Here we use Signal Detection Theory to formulate and compare various models of cue-combination, many of which are commonly used to explain empirical data. We alert the reader to the key assumptions inherent in each model, and provide formulas for deriving quantitative predictions. Code is also provided for simulating each model, allowing expected levels of measurement error to be quantified. Based on these results, it is shown that predicted sensitivity often differs surprisingly little between qualitatively distinct models of combination. This means that sensitivity alone is not sufficient for understanding decision efficiency, and the implications of this are discussed
End-point of the rp process and periodic gravitational wave emission
The general end-point of the rp process in rapidly accreting neutron stars is
believed to be a surface distribution of matter whose nuclear composition may
depend on position. Its evolution during compression beyond the neutron-drip
threshold density is determined by the presence of nuclear formation enthalpy
minima at the proton closed shells. At threshold, a sequence of weak
interactions with capture or emission of neutron pairs rapidly transform nuclei
to the most accessible proton closed shell. Therefore, angular asymmetries in
nuclear composition present in accreted matter at neutron drip are preserved
during further compression to higher densities provided transition rates
between closed shells are negligible. Although it has been confirmed that this
condition is satisfied for predicted internal temperatures and for the
formation enthalpy distribution used in this work, it would not be so if the
true enthalpy differences between maxima and minima in the distribution were a
factor of two smaller. For this reason, it does not appear possible to assert
with any confidence that position-dependent surface composition can lead to
significant angle-dependence of the equation of state and to potentially
observable gravitational radiation. The effect of non-radial internal
temperature gradients on angle-dependency of the equation of state is also not
quantifiable.Comment: This version corrects a major error in estimating the effect of
composition asymmetry on the equation of state. Its conclusions are less
definite than those of the previous version. 9 pages RevTex; 1 figure. To be
published in Phys. Rev.
Working with the given
In this essay the author suggests that although the resulting architectural style may be ambiguous, a dialogue with an existing place can be creative, rewarding and appropriate
Heteroatom-doped hydrogenated amorphous carbons, a-C:H:X 'Volatile' silicon, sulphur and nitrogen depletion, blue photoluminescence, diffuse interstellar bands and ferro-magnetic carbon grain connections (Research Note)
Context. Hydrogenated amorphous carbons, a-C:H, can incorporate a variety of
heteroatoms, which can lead to interesting effects. Aims. To investigate the
doping of interstellar a-C:H grains with, principally, Si, O, N and S atoms
within the astrophysical context. Methods. A search of the literature on doped
a-C:H reveals a number of interesting phenomena of relevance to astrophysics.
Results. X dopants in a-C:H:X materials can affect the sp3/sp2 ratio (X = Si, O
and N), lead to blue photoluminescence (undoped or X = N), induce
ferromagnetic-like behaviour (X = N and S) or simply be incorporated (depleted)
into the structure (X = Si, O, N and S). Si and N atoms could also incorporate
into fullerenes, possibly forming colour-centres that could mimic diffuse
interstellar bands. Conclusions. Doped a-C:H grains could explain several
dust-related conundrums, such as: 'volatile' Si in photo-dissociation regions,
S and N depletion in molecular clouds, blue luminescence, some diffuse
interstellar bands and ferromagnetism in carbonaceous grains.Comment: 5 page
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