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Grinnell, IA, United States

Grinnell College is a private liberal arts college in Grinnell, Iowa, U.S. known for its rigorous academics and tradition of social responsibility. It was founded in 1846, when a group of New England Congregationalists established the Trustees of Iowa College.In its 2014 edition of "America's Best Colleges", U.S. News & World Report ranked Grinnell 17th among all liberal arts colleges in the United States, and third highest for economic diversity as measured by low-income students receiving federal Pell Grants. Grinnell had an acceptance rate of 27 percent in 2014. Wikipedia.

Blanchard J.D.,Grinnell College | Tanner J.,University of Oxford
Mathematical Programming Computation | Year: 2013

For appropriate matrix ensembles, greedy algorithms have proven to be an efficient means of solving the combinatorial optimization problem associated with compressed sensing. This paper describes an implementation for graphics processing units (GPU) of hard thresholding, iterative hard thresholding, normalized iterative hard thresholding, hard thresholding pursuit, and a two-stage thresholding algorithm based on compressive sampling matching pursuit and subspace pursuit. The GPU acceleration of the former bottleneck, namely the matrix-vector multiplications, transfers a significant portion of the computational burden to the identification of the support set. The software solves high-dimensional problems in fractions of a second which permits large-scale testing at dimensions currently unavailable in the literature. The GPU implementations exhibit up to 70× acceleration over standard Matlab central processing unit implementations using automatic multi-threading. © Springer-Verlag Berlin Heidelberg and Mathematical Optimization Society 2013.

Brouhle K.,Grinnell College | Khanna M.,University of Illinois at Urbana - Champaign
Ecological Economics | Year: 2012

This paper analyzes the determinants of demand for Nordic Swan eco-labeled paper products and whether the factors determining the discrete decision to buy a Swan-labeled product are different from those that determine the quantity purchased. Using observed consumer purchase data from Denmark, we find that prices and socio-demographic characteristics have a strong impact on the decision to purchase a Swan-labeled good. The quantity consumed of Swan-labeled goods, on the other hand, is strongly affected by the availability of Swan goods, discounts, and household size. © 2011 Elsevier B.V.

Rauscher E.,Princeton University | Kempton E.M.R.,Grinnell College
Astrophysical Journal | Year: 2014

We study the feasibility of observationally constraining the rotation rate of hot Jupiters, planets that are typically assumed to have been tidally locked into synchronous rotation. We use a three-dimensional General Circulation Model to solve for the atmospheric structure of two hot Jupiters (HD 189733b and HD 209458b), assuming rotation periods that are 0.5, 1, or 2 times their orbital periods (2.2 and 3.3 days, respectively), including the effect of variable stellar heating. We compare two observable properties: (1) the spatial variation of flux emitted by the planet, measurable in orbital phase curves, and (2) the net Doppler shift in transmission spectra of the atmosphere, which is tantalizingly close to being measurable in high-resolution transit spectra. Although we find little difference between the observable properties of the synchronous and non-synchronous models of HD 189733b, we see significant differences when we compare the models of HD 209458b. In particular, the slowly rotating model of HD 209458b has an atmospheric circulation pattern characterized by westward flow and an orbital phase curve that peaks after secondary eclipse (in contrast to all of our other models), while the quickly rotating model has a net Doppler shift that is more strongly blueshifted than the other models. Our results demonstrate that the combined use of these two techniques may be a fruitful way to constrain the rotation rate of some planets and motivate future work on this topic. © 2014. The American Astronomical Society. All rights reserved..

Kelty-Stephen D.G.,Grinnell College | Dixon J.A.,University of Connecticut
Journal of Experimental Psychology: Human Perception and Performance | Year: 2014

Intermodal integration required for perceptual learning tasks is rife with individual differences. Participants vary in how they use perceptual information to one modality. One participant alone might change her own response over time. Participants vary further in their use of feedback through one modality to inform another modality. Two experiments test the general hypothesis that perceptual-motor fluctuations reveal both information use within modality and coordination among modalities. Experiment 1 focuses on perceptual learning in dynamic touch, in which participants use exploratory hand-wielding of unseen objects to make visually guided length judgments and use visual feedback to rescale their judgments of the same mechanical information. Previous research found that the degree of fractal temporal scaling (i.e., "fractality") in hand-wielding moderates the use of mechanical information. Experiment 1 shows that head-sway fractality moderates the use of visual information. Further, experience with feedback increases head-sway fractality and prolongs its effect on later hand-wielding fractality. Experiment 2 replicates effects of head-sway fractality moderating use of visual information in a purely visualjudgment task. Together, these findings suggest that fractal fluctuations may provide a modal-general window onto not just how participants use perceptual information but also how well they may integrate information among different modalities. © 2014 American Psychological Association.

DiMattina C.,Grinnell College
Journal of vision | Year: 2012

Occlusion boundaries and junctions provide important cues for inferring three-dimensional scene organization from two-dimensional images. Although several investigators in machine vision have developed algorithms for detecting occlusions and other edges in natural images, relatively few psychophysics or neurophysiology studies have investigated what features are used by the visual system to detect natural occlusions. In this study, we addressed this question using a psychophysical experiment where subjects discriminated image patches containing occlusions from patches containing surfaces. Image patches were drawn from a novel occlusion database containing labeled occlusion boundaries and textured surfaces in a variety of natural scenes. Consistent with related previous work, we found that relatively large image patches were needed to attain reliable performance, suggesting that human subjects integrate complex information over a large spatial region to detect natural occlusions. By defining machine observers using a set of previously studied features measured from natural occlusions and surfaces, we demonstrate that simple features defined at the spatial scale of the image patch are insufficient to account for human performance in the task. To define machine observers using a more biologically plausible multiscale feature set, we trained standard linear and neural network classifiers on the rectified outputs of a Gabor filter bank applied to the image patches. We found that simple linear classifiers could not match human performance, while a neural network classifier combining filter information across location and spatial scale compared well. These results demonstrate the importance of combining a variety of cues defined at multiple spatial scales for detecting natural occlusions.

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