1,699 research outputs found
Cortical Computation of Stereo Disparity
Our ability to see the world in depth is a major accomplishment of the brain. Previous models of how positionally disparate cues to the two eyes are binocularly matched limit possible matches by invoking uniqueness and continuity constraints. These approaches cannot explain data wherein uniqueness fails and changes in contrast alter depth percepts, or where surface discontinuities cause surfaces to be seen in depth although they are registered by only one eye (da Vinci stereopsis). A new stereopsis model explains these depth percepts by proposing how cortical complex cells binocularly filter their inputs and how monocular and binocular complex cells compete to determine the winning depth signals.Defense Advanced Research Projects Agency (N00014-92-J-4015); Air Force Office of Scientific Research (90-0175); Office of Naval Research (N00014-91-J-4100); James S. McDonnell Foundation (94-40); Defense Advanced Research Projects Agency and the Office of Naval Research (N00014-95-1-0409, N00014-95-1-0657
Locomotor activity rhythms and photoperiodic time-measurement in the blowfly Calliphora vicina R-D
When the going gets rough – studying the effect of surface roughness on the adhesive abilities of tree frogs
Tree frogs need to adhere to surfaces of various roughnesses in their natural habitats; these include bark, leaves and rocks. Rough
surfaces can alter the effectiveness of their toe pads, due to factors such as a change of real contact area and abrasion of the pad
epithelium. Here, we tested the effect of surface roughness on the attachment abilities of the tree frog Litoria caerulea. This was
done by testing shear and adhesive forces on artificial surfaces with controlled roughness, both on single toe pads and whole animal
scales. It was shown that frogs can stick 2–3 times better on small scale roughnesses (3–6 µm asperities), producing higher adhesive
and frictional forces, but relatively poorly on the larger scale roughnesses tested (58.5–562.5 µm asperities). Our experiments
suggested that, on such surfaces, the pads secrete insufficient fluid to fill the space under the pad, leaving air pockets that would
significantly reduce the Laplace pressure component of capillarity. Therefore, we measured how well the adhesive toe pad would
conform to spherical asperities of known sizes using interference reflection microscopy. Based on experiments where the conformation
of the pad to individual asperities was examined microscopically, our calculations indicate that the pad epithelium has a low
elastic modulus, making it highly deformable
Academic Service Learning and Society: From Individual to Institutional
This paper examines how Academic Service Learning (ASL) has gone from being an initiative by individual faculty to being institutionalized by universities as means to promote learning, pursue mission, and impact society. It outlines various uses of ASL by individual faculty and examines its progression into a university sponsored service-learning vessel of vision and mission. Its use acknowledges the interconnectedness of universities and society and emphasizes the need and obligation that universities feel, or should feel, in contributing to the betterment of the world we live in. In terms of being a university-sponsored initiative it highlights its use in the business curriculum of a large university in the northeast United States. This article recommends that ASL is an easily instituted method of teaching in many disciplines and is of benefit to multiple constituents both internally and externally to academic institutions
Sufficient Conditions for Apparent Horizons in Spherically Symmetric Initial Data
We establish sufficient conditions for the appearance of apparent horizons in
spherically symmetric initial data when spacetime is foliated extrinsically.
Let and be respectively the total material energy and the total
material current contained in some ball of radius . Suppose that the
dominant energy condition is satisfied. We show that if then
the region must possess a future apparent horizon for some non -trivial closed
subset of such gauges. The same inequality holds on a larger subset of gauges
but with a larger constant of proportionality which depends weakly on the
gauge. This work extends substantially both our joint work on moment of time
symmetry initial data as well as the work of Bizon, Malec and \'O Murchadha on
a maximal slice.Comment: 16 pages, revtex, to appear in Phys. Rev.
Embedding spherical spacelike slices in a Schwarzschild solution
Given a spherical spacelike three-geometry, there exists a very simple
algebraic condition which tells us whether, and in which, Schwarzschild
solution this geometry can be smoothly embedded. One can use this result to
show that any given Schwarzschild solution covers a significant subset of
spherical superspace and these subsets form a sequence of nested domains as the
Schwarzschild mass increases. This also demonstrates that spherical data offer
an immediate counter example to the thick sandwich `theorem'
A Gut Feeling about GABA: Focus on GABAB Receptors
γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the body and hence GABA-mediated neurotransmission regulates many physiological functions, including those in the gastrointestinal (GI) tract. GABA is located throughout the GI tract and is found in enteric nerves as well as in endocrine-like cells, implicating GABA as both a neurotransmitter and an endocrine mediator influencing GI function. GABA mediates its effects via GABA receptors which are either ionotropic GABAA or metabotropic GABAB. The latter which respond to the agonist baclofen have been least characterized, however accumulating data suggest that they play a key role in GI function in health and disease. Like GABA, GABAB receptors have been detected throughout the gut of several species in the enteric nervous system, muscle, epithelial layers as well as on endocrine-like cells. Such widespread distribution of this metabotropic GABA receptor is consistent with its significant modulatory role over intestinal motility, gastric emptying, gastric acid secretion, transient lower esophageal sphincter relaxation and visceral sensation of painful colonic stimuli. More intriguing findings, the mechanisms underlying which have yet to be determined, suggest GABAB receptors inhibit GI carcinogenesis and tumor growth. Therefore, the diversity of GI functions regulated by GABAB receptors makes it a potentially useful target in the treatment of several GI disorders. In light of the development of novel compounds such as peripherally acting GABAB receptor agonists, positive allosteric modulators of the GABAB receptor and GABA producing enteric bacteria, we review and summarize current knowledge on the function of GABAB receptors within the GI tract
Bowen-York trumpet data and black-hole simulations
The most popular method to construct initial data for black-hole-binary
simulations is the puncture method, in which compactified wormholes are given
linear and angular momentum via the Bowen-York extrinsic curvature. When these
data are evolved, they quickly approach a ``trumpet'' topology, suggesting that
it would be preferable to use data that are in trumpet form from the outset. To
achieve this, we extend the puncture method to allow the construction of
Bowen-York trumpets, including an outline of an existence and uniqueness proof
of the solutions. We construct boosted, spinning and binary Bowen-York puncture
trumpets using a single-domain pseudospectral elliptic solver, and evolve the
binary data and compare with standard wormhole-data results. We also show that
for boosted trumpets the black-hole mass can be prescribed {\it a priori},
without recourse to the iterative procedure that is necessary for wormhole
data.Comment: 15 pages, 14 figures. Published versio
- …