7,486 research outputs found
Comment: Struggles with Survey Weighting and Regression Modeling
Comment: Struggles with Survey Weighting and Regression Modeling
[arXiv:0710.5005]Comment: Published in at http://dx.doi.org/10.1214/088342307000000177 the
Statistical Science (http://www.imstat.org/sts/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Simulating the nanomechanical response of cyclooctatetraene molecules on a graphene device
We investigate the atomic and electronic structures of cyclooctatetraene
(COT) molecules on graphene and analyze their dependence on external gate
voltage using first-principles calculations. The external gate voltage is
simulated by adding or removing electrons using density functional theory (DFT)
calculations. This allows us to investigate how changes in carrier density
modify the molecular shape, orientation, adsorption site, diffusion barrier,
and diffusion path. For increased hole doping COT molecules gradually change
their shape to a more flattened conformation and the distance between the
molecules and graphene increases while the diffusion barrier drastically
decreases. For increased electron doping an abrupt transition to a planar
conformation at a carrier density of -810 e/cm is observed.
These calculations imply that the shape and mobility of adsorbed COT molecules
can be controlled by externally gating graphene devices
The Local Structure of Space-Variant Images
Local image structure is widely used in theories of both machine and biological vision. The form of the differential operators describing this structure for space-invariant images has been well documented (e.g. Koenderink, 1984). Although space-variant coordinates are universally used in mammalian visual systems, the form of the operators in the space-variant domain has received little attention. In this report we derive the form of the most common differential operators and surface characteristics in the space-variant domain and show examples of their use. The operators include the Laplacian, the gradient and the divergence, as well as the fundamental forms of the image treated as a surface. We illustrate the use of these results by deriving the space-variant form of corner detection and image enhancement algorithms. The latter is shown to have interesting properties in the complex log domain, implicitly encoding a variable grid-size integration of the underlying PDE, allowing rapid enhancement of large scale peripheral features while preserving high spatial frequencies in the fovea.Office of Naval Research (N00014-95-I-0409
Real-Time Anisotropic Diffusion using Space-Variant Vision
Many computer and robot vision applications require multi-scale image analysis. Classically, this has been accomplished through the use of a linear scale-space, which is constructed by convolution of visual input with Gaussian kernels of varying size (scale). This has been shown to be equivalent to the solution of a linear diffusion equation on an infinite domain, as the Gaussian is the Green's function of such a system (Koenderink, 1984). Recently, much work has been focused on the use of a variable conductance function resulting in anisotropic diffusion described by a nonlinear partial differential equation (PDF). The use of anisotropic diffusion with a conductance coefficient which is a decreasing function of the gradient magnitude has been shown to enhance edges, while decreasing some types of noise (Perona and Malik, 1987). Unfortunately, the solution of the anisotropic diffusion equation requires the numerical integration of a nonlinear PDF which is a costly process when carried out on a fixed mesh such as a typical image. In this paper we show that the complex log transformation, variants of which are universally used in mammalian retino-cortical systems, allows the nonlinear diffusion equation to be integrated at exponentially enhanced rates due to the non-uniform mesh spacing inherent in the log domain. The enhanced integration rates, coupled with the intrinsic compression of the complex log transformation, yields a seed increase of between two and three orders of magnitude, providing a means of performing real-time image enhancement using anisotropic diffusion.Office of Naval Research (N00014-95-I-0409
A Spectral Network Model of Pitch Perception
A model of pitch perception, called the Spatial Pitch Network or SPINET model, is developed and analyzed. The model neurally instantiates ideas front the spectral pitch modeling literature and joins them to basic neural network signal processing designs to simulate a broader range of perceptual pitch data than previous spectral models. The components of the model arc interpreted as peripheral mechanical and neural processing stages, which arc capable of being incorporated into a larger network architecture for separating multiple sound sources in the environment.
The core of the new model transforms a spectral representation of an acoustic source into a spatial distribution of pitch strengths. The SPINET model uses a weighted "harmonic sieve" whereby the strength of activation of a given pitch depends upon a weighted sum of narrow regions around the harmonics of the nominal pitch value, and higher harmonics contribute less to a pitch than lower ones. Suitably chosen harmonic weighting functions enable computer simulations of pitch perception data involving mistuned components, shifted harmonics, and various types of continuous spectra including rippled noise. It is shown how the weighting functions produce the dominance region, how they lead to octave shifts of pitch in response to ambiguous stimuli, and how they lead to a pitch region in response to the octave-spaced Shepard tone complexes and Deutsch tritones without the use of attentional mechanisms to limit pitch choices. An on-center off-surround network in the model helps to produce noise suppression, partial masking and edge pitch. Finally, it is shown how peripheral filtering and short term energy measurements produce a model pitch estimate that is sensitive to certain component phase relationships.Air Force Office of Scientific Research (F49620-92-J-0225); American Society for Engineering Educatio
Recall in Washington: A Time for Reform
The purpose of this article is threefold: (1) to trace the history of recall in Washington, including the enactment of our present recall statutes and their fundamental principles; (2) to examine the reasons behind the apparent judicial retreat from those principles; and (3) to propose amendments to the present recall statutes to implement the constitutional intent
Self-referential cognition and empathy in autism.
BACKGROUND: Individuals with autism spectrum conditions (ASC) have profound impairments in the interpersonal social domain, but it is unclear if individuals with ASC also have impairments in the intrapersonal self-referential domain. We aimed to evaluate across several well validated measures in both domains, whether both self-referential cognition and empathy are impaired in ASC and whether these two domains are related to each other. METHODOLOGY/PRINCIPAL FINDINGS: Thirty adults aged 19-45, with Asperger Syndrome or high-functioning autism and 30 age, sex, and IQ matched controls participated in the self-reference effect (SRE) paradigm. In the SRE paradigm, participants judged adjectives in relation to the self, a similar close other, a dissimilar non-close other, or for linguistic content. Recognition memory was later tested. After the SRE paradigm, several other complimentary self-referential cognitive measures were taken. Alexithymia and private self-consciousness were measured via self-report. Self-focused attention was measured on the Self-Focus Sentence Completion task. Empathy was measured with 3 self-report instruments and 1 performance measure of mentalizing (Eyes test). Self-reported autistic traits were also measured with the Autism Spectrum Quotient (AQ). Although individuals with ASC showed a significant SRE in memory, this bias was decreased compared to controls. Individuals with ASC also showed reduced memory for the self and a similar close other and also had concurrent impairments on measures of alexithymia, self-focused attention, and on all 4 empathy measures. Individual differences in self-referential cognition predicted mentalizing ability and self-reported autistic traits. More alexithymia and less self memory was predictive of larger mentalizing impairments and AQ scores regardless of diagnosis. In ASC, more self-focused attention is associated with better mentalizing ability and lower AQ scores, while in controls, more self-focused attention is associated with decreased mentalizing ability and higher AQ scores. Increasing private self-consciousness also predicted better mentalizing ability, but only for individuals with ASC. CONCLUSIONS/SIGNIFICANCE: We conclude that individuals with ASC have broad impairments in both self-referential cognition and empathy. These two domains are also intrinsically linked and support predictions made by simulation theory. Our results also highlight a specific dysfunction in ASC within cortical midlines structures of the brain such as the medial prefrontal cortex
Why corals care about ocean acidification : uncovering the mechanism
Author Posting. © Oceanography Society, 2009. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 22 no. 4 (2009): 118-127.Stony corals build hard skeletons of calcium carbonate (CaCO3) by
combining calcium with carbonate ions derived, ultimately, from seawater. The
concentration of carbonate ions relative to other carbonate species in seawater
is rather low, so corals expend energy to raise the pH of seawater sequestered in
an isolated, extracellular compartment where crystal growth occurs. This action
converts plentiful bicarbonate ions to the carbonate ions required for calcification,
allowing corals to produce CaCO3 about 100 times faster than it could otherwise
form. It is this rapid and efficient production of CaCO3 crystals that enables
corals to build coral reefs.
Ocean acidification reduces the pH and thus the abundance of carbonate ions in
seawater. Corals living in acidified seawater continue to produce CaCO3 and expend
as much energy as their counterparts in normal seawater to raise the pH of the calcifying
fluid. However, in acidified seawater, corals are unable to elevate the concentration
of carbonate ions to the level required for normal skeletal growth. In several
experiments, we found that boosting the energetic status of corals by enhanced
heterotrophic feeding or moderate increases in inorganic nutrients helped to offset
the negative impact of ocean acidification. However, this built-in defense is unlikely
to benefit corals as levels of CO2 in the atmosphere continue to rise. Most climate
models predict that the availability of inorganic nutrients and plankton in the surface
waters where corals live will decrease as a consequence of global warming. Thus,
corals and coral reefs may be significantly more vulnerable to ocean acidification
than previously thought.Anne L. Cohen
acknowledges support from the WHOI
Directorate for our Marine Calcification
and Culture Labs, from WHOI’s Ocean
Life and Tropical Research Institutes,
and from NSF CO-0648157. Michael
Holcomb’s graduate research was
supported in part by an NSF graduate
student fellowship, an MIT Presidential
Award, and an International Coral Reef
Society fellowship
The Extremely Red Objects Found Thus Far in the Caltech Faint Galaxy Redshift Survey
We discuss the very red objects found in the first field of the Caltech Faint
Galaxy Redshift Survey, for which the observations and analysis are now
complete. In this field, which is 15 arcmin and at J005325+1234 there are
195 objects with mag, of which 84% have redshifts. The sample
includes 24 spectroscopically confirmed Galactic stars, 136 galaxies, three
AGNs, and 32 objects without redshifts.
About 10% of the sample has mag. Four of these objects have
redshifts, with . Three of these are based on absorption
features in the mid-UV, while the lowest redshift object shows the standard
features near 4000\AA. Many of the objects still without redshifts have been
observed spectroscopically, and no emission lines were seen in their spectra.
We believe they are galaxies with that are red due to their
age and stellar content and not to some large amount of internal reddening from
dust.
Among the many other results from this survey of interest here is a
determination of the median extinction in the mid-UV for objects with strong
emission line spectra at . The result is extinction by a factor
of 2 at 2400\AA.Comment: 6 pages, Latex, with 2 figures. To be published in the proceedings of
the conference "Infrared Surveys: A Prelude to SIRTF
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