66,727 research outputs found
Recommended from our members
The function of photomechanical movements in the retina of the rainbow trout (Salmo gairdneri)
1. The function of photomechanical movements in the retina of rainbow trout (Salmo gairdneri) was investigated by determining both the effect of light on the level of extractable visual pigment, and the electroretinographic b-wave sensitivity, during various stages of photomechanical light and dark adaptation.
2. Dark-adapted fish, light-adapted fish, and dark-adapted fish exposed to ten minutes direct sunlight had on average visual pigment concentrations of 100, 82 and 36% respectively.
3. The intensity of illumination required to bleach a specified amount of visual pigment in the light-adapted retina was found to be 1.29 log units higher than that needed to bleach the same amount of visual pigment in a dark-adapted eye.
4. The level of extractable visual pigment was observed to be relatively constant over natural twilight periods.
5. A close temporal correlation was observed between the time course of electroretinographic adaptation, measured by the b-wave sensitivity, and photomechanical changes.
6. All these observations tend to support the hypothesis that photomechanical movements serve, at least in part, to protect the rod visual pigment from overstimulation in the light-adapted retina
Effective potential and warp factor dynamics
We define an effective potential describing all massless and massive modes in
the supergravity limit of string/M theory compactification which is valid
off-shell, i.e. without imposing the equations of motion. If we neglect the
warp factor, it is unbounded below, as is the case for the action in Euclidean
quantum gravity. By study of the constraint which determines the warp factor,
we solve this problem, obtaining a physically satisfying and tractable
description of the dynamics of the warp factor.Comment: 32 pages, JHEP3.cls. v4: added reference to hep-th/050715
Basic results in Vacuum Statistics
A review of recent work on constructing and finding statistics of string
theory vacua, done in collaboration with Frederik Denef, Bogdan Florea, Bernard
Shiffman and Steve Zelditch.Comment: 11 pages, 5 figures (Latex elsart.cls, included
Unifying discrete and continuous Weyl-Titchmarsh theory via a class of linear Hamiltonian systems on Sturmian time scales
In this study, we are concerned with introducing Weyl-Titchmarsh theory for a
class of dynamic linear Hamiltonian nabla systems over a half-line on Sturmian
time scales. After developing fundamental properties of solutions and regular
spectral problems, we introduce the corresponding maximal and minimal operators
for the system. Matrix disks are constructed and proved to be nested and
converge to a limiting set. Some precise relationships among the rank of the
matrix radius of the limiting set, the number of linearly independent square
summable solutions, and the defect indices of the minimal operator are
established. Using the above results, a classification of singular dynamic
linear Hamiltonian nabla systems is given in terms of the defect indices of the
minimal operator, and several equivalent conditions on the cases of limit point
and limit circle are obtained, respectively. These results unify and extend
certain classic and recent results on the subject in the continuous and
discrete cases, respectively, to Sturmian time scales.Comment: 34 page
Enhanced Gauge Symmetry in M(atrix) Theory
We discuss the origin of enhanced gauge symmetry in ALE (and K3)
compactification of M theory, either defined as the strong coupling limit of
the type IIa superstring, or as defined by Banks et al. In the D-brane
formalism, wrapped membranes are D0 branes with twisted string boundary
conditions, and appear on the same footing with the Kaluza-Klein excitations of
the gauge bosons. In M(atrix) theory, the construction appears to work for
arbitrary ALE metric.Comment: 10 pp, harvma
Some Comments on QCD String
We try to draw lessons for higher dimensions from the string representations
recently derived for large Yang-Mills theory by Gross and Taylor, Kostov,
and others, and call attention to three characteristics that should be expected
of a string theory precisely equivalent to a higher dimensional gauge theory:
continuous world-sheets; strong coupling at short distances; and negative
weights. To appear in the proceedings of the Strings '93 Berkeley conference.Comment: RU-94-9. (harvmac, 9 pp.
- …