The Timing of Visual Object Categorization

An object can be categorized at different levels of abstraction: as natural or man-made, animal or plant, bird or dog, or as a Northern Cardinal or Pyrrhuloxia. There has been growing interest in understanding how quickly categorizations at different levels are made and how the timing of those perceptual decisions changes with experience. We specifically contrast two perspectives on the timing of object categorization at different levels of abstraction. By one account, the relative timing implies a relative timing of stages of visual processing that are tied to particular levels of object categorization: Fast categorizations are fast because they precede other categorizations within the visual processing hierarchy. By another account, the relative timing reflects when perceptual features are available over time and the quality of perceptual evidence used to drive a perceptual decision process: Fast simply means fast, it does not mean first. Understanding the short-term and long-term temporal dynamics of object categorizations is key to developing computational models of visual object recognition. We briefly review a number of models of object categorization and outline how they explain the timing of visual object categorization at different levels of abstraction

Scaling in the Positive Plaquette Model and Universality in SU(2) Lattice Gauge Theory

We investigate universality, scaling, the beta-function and the topological charge in the positive plaquette model for SU(2) lattice gauge theory. Comparing physical quantities, like the critical temperature, the string tension, glueball masses, and their ratios, we explore the effect of a complete suppression of a certain lattice artifact, namely the negative plaquettes, for SU(2) lattice gauge theory. Our result is that this modification does not change the continuum limit, i.e., the universality class. The positive plaquette model and the standard Wilson formulation describe the same physical situation. The approach to the continuum limit given by the beta-function in terms of the bare lattice coupling, however, is rather different: the beta-function of the positive plaquette model does not show a dip like the model with standard Wilson action.Comment: 35 pages, preprint numbers FSU-SCRI-94-71 and HU Berlin-IEP-94/1

Some Cautionary Remarks on Abelian Projection and Abelian Dominance

Some critical remarks are presented, concerning the abelian projection theory of quark confinement.Comment: Talk presented at LATTICE96(topology) plenary session, uses psfig and espcrc2 package

Universality, Scaling and Topology with a Modified Lattice Action

We examined the effect of a complete suppression of a lattice artifact, the negative plaquettes, on physical quantities, such as the critical temperature, the string tension, the topological charge, glueball masses, and their ratios.Comment: 3 pages, self unpacking uuencoded PostScript file, contribution to conference LATTICE '9

Real-Time Maps of Fluid Flow Fields in Porous Biomaterials

Mechanical forces such as fluid shear have been shown to enhance cell growth and differentiation, but knowledge of their mechanistic effect on cells is limited because the local flow patterns and associated metrics are not precisely known. Here we present real-time, noninvasive measures of local hydrodynamics in 3D biomaterials based on nuclear magnetic resonance. Microflow maps were further used to derive pressure, shear and fluid permeability fields. Finally, remodeling of collagen gels in response to precise fluid flow parameters was correlated with structural changes. It is anticipated that accurate flow maps within 3D matrices will be a critical step towards understanding cell behavior in response to controlled flow dynamics.Comment: 23 pages, 4 figure

Spatial population expansion promotes the evolution of cooperation in an experimental Prisoner's Dilemma

Cooperation is ubiquitous in nature, but explaining its existence remains a central interdisciplinary challenge. Cooperation is most difficult to explain in the Prisoner's Dilemma game, where cooperators always lose in direct competition with defectors despite increasing mean fitness. Here we demonstrate how spatial population expansion, a widespread natural phenomenon, promotes the evolution of cooperation. We engineer an experimental Prisoner's Dilemma game in the budding yeast Saccharomyces cerevisiae to show that, despite losing to defectors in nonexpanding conditions, cooperators increase in frequency in spatially expanding populations. Fluorescently labeled colonies show genetic demixing of cooperators and defectors, followed by increase in cooperator frequency as cooperator sectors overtake neighboring defector sectors. Together with lattice-based spatial simulations, our results suggest that spatial population expansion drives the evolution of cooperation by (1) increasing positive genetic assortment at population frontiers and (2) selecting for phenotypes maximizing local deme productivity. Spatial expansion thus creates a selective force whereby cooperator-enriched demes overtake neighboring defector-enriched demes in a "survival of the fastest". We conclude that colony growth alone can promote cooperation and prevent defection in microbes. Our results extend to other species with spatially restricted dispersal undergoing range expansion, including pathogens, invasive species, and humans

Dissolved iron transport pathways in the Ross Sea : influence of tides and horizontal resolution in a regional ocean model

© The Author(s), 2016. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Journal of Marine Systems 166 (2017): 73-86, doi:10.1016/j.jmarsys.2016.10.008.Phytoplankton production in the Ross Sea is regulated by the availability of dissolved iron (dFe), a limiting micro-nutrient, whose sources include Circumpolar Deep Water, sea ice melt, glacial melt, and benthic sources (sediment efflux and remineralization). We employ a passive tracer dye to model the benthic dFe sources and track pathways from deep areas of the continental shelf to the surface mixed layer in simulations with and without tidal forcing, and at 5 and 1.5km horizontal resolution. This, combined with dyes for each of the other dFe sources, provides an estimate of total dFe supply to surface waters. We find that tidal forcing increases the amount of benthic dye that covers the banks on the continental shelf. Calculations of mixed layer depth to define the surface ocean give similar average values over the shelf, but spatial patterns differ between simulations, particularly along the ice shelf front. Benthic dFe supply in simulations shows an increase with tidal forcing and a decrease with higher resolution. The changes in benthic dFe supply control the difference in total supply between simulations. Overall, the total dFe supply from simulations varies from 5.60 to 7.95 μmol m-2 yr-1, with benthic supply comprising 32-50%, comparing well with recent data and model synthesis. We suggest that including tides and using high horizontal resolution is important, especially when considering spatial variability of iron supply on the Ross Sea shelf.The authors acknowledge funding from NSF's Antarctic Research Program 496 (ODU: ANT-0944174; WHOI: ANT-0094165)

Modeling ocean eddies on Antarctica's cold water continental shelves and their effects on ice shelf basal melting

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research-Oceans 124(7), (2019): 5067-5084, doi: 10.1029/2018JC014688.Changes in the rate of ocean‐driven basal melting of Antarctica's ice shelves can alter the rate at which the grounded ice sheet loses mass and contributes to sea level change. Melt rates depend on the inflow of ocean heat, which occurs through steady circulation and eddy fluxes. Previous studies have demonstrated the importance of eddy fluxes for ice shelves affected by relatively warm intrusions of Circumpolar Deep Water. However, ice shelves on cold water continental shelves primarily melt from dense shelf water near the grounding line and from light surface water at the ice shelf front. Eddy effects on basal melt of these ice shelves have not been studied. We investigate where and when a regional ocean model of the Ross Sea resolves eddies and determine the effect of eddy processes on basal melt. The size of the eddies formed depends on water column stratification and latitude. We use simulations at horizontal grid resolutions of 5 and 1.5 km and, in the 1.5‐km model, vary the degree of topography smoothing. The higher‐resolution models generate about 2–2.5 times as many eddies as the low‐resolution model. In all simulations, eddies cross the ice shelf front in both directions. However, there is no significant change in basal melt between low‐ and high‐resolution simulations. We conclude that higher‐resolution models (<1 km) are required to better represent eddies in the Ross Sea but hypothesize that basal melt of the Ross Ice Shelf is relatively insensitive to our ability to fully resolve the eddy field.This research was funded by NSF's Antarctic Research Program (ANT‐0944174, ANT‐0944165, and ANT‐1443677), Ocean Sciences Program (OCE‐1357522), and by the Future of Ice Initiative at the University of Washington. It was supported by the Turing High Performance Computing Cluster at Old Dominion University. S. M. acknowledges the support of her dissertation committee. Portions of this work appear in S. M.'s PhD thesis. The eddy tracking code and specific version of ROMS are on S. M.'s github (https://github.com/mnemoniko). Forcing files to run the simulations described are in three separate records on zenodo.org under DOIs 10.5281/zenodo.2649541, 10.5281/zenodo.2649547, and 10.5281/zenodo.2650294. We thank three anonymous reviewers for their helpful suggestions.2020-01-0

Charge Screening, Large-N, and the Abelian Projection Model of Confinement

We point out that the abelian projection theory of quark confinement is in conflict with certain large-N predictions. According to both large-N and lattice strong-coupling arguments, the perimeter law behavior of adjoint Wilson loops at large scales is due to charge-screening, and is suppressed relative to the area term by a factor of $1/N^2$. In the abelian projection theory, however, the perimeter law is due to the fact that $N-1$ out of $N^2-1$ adjoint quark degrees of freedom are (abelian) neutral and unconfined; the suppression factor relative to the area law is thus only $1/N$. We study numerically the behavior of Wilson loops and Polyakov lines with insertions of (abelian) charge projection operators, in maximal abelian gauge. It appears from our data that the forces between abelian charged, and abelian neutral adjoint quarks are not significantly different. We also show via the lattice strong-coupling expansion that, at least at strong couplings, QCD flux tubes attract one another, whereas vortices in type II superconductors repel.Comment: 20 pages (Latex), 8 figures, IFUP-TH 54/9

Free energy of an SU(2) monopole-antimonopole pair

We present a high-statistic numerical study of the free energy of a monopole-antimonopole pair in pure SU(2) theory. We find that the monopole-antimonopole interaction potential exhibits a screened behavior, as one would expect in presence of a monopole condensate. Screening occurs both in the low-temperature, confining phase of the theory, and in the high-temperature deconfined phase, with no evidence of a discontinuity of the screening mass across the transition. The mass of the object responsible for the screening at low temperature is approximately twice the established value for the lightest glueball, indicating a prevalent coupling to glueball excitations. At high temperature, the screening mass increases. We contrast the behavior of the quantum system with that of the corresponding classical system, where the monopole-antimonopole potential is of the Coulomb type.Comment: Latex, 22 pages, 8 figures. A mistake in the computer program implementing the multihistogram method has been corrected and all the affected numerical data have been revised. The main conclusions of the paper are unchanged, but the screening masses turn out somehow larger. (We thank Philippe de Forcrand for correspondence which helped us find the error.