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Inhibitory effects of soluble fibronectin fractions on cultured neurones
No abstract available
Fast Algorithm for Partial Covers in Words
A factor of a word is a cover of if every position in lies
within some occurrence of in . A word covered by thus
generalizes the idea of a repetition, that is, a word composed of exact
concatenations of . In this article we introduce a new notion of
-partial cover, which can be viewed as a relaxed variant of cover, that
is, a factor covering at least positions in . We develop a data
structure of size (where ) that can be constructed in time which we apply to compute all shortest -partial covers for a
given . We also employ it for an -time algorithm computing
a shortest -partial cover for each
Properties of visual field defects around the monocular preferred retinal locus in age-related macular degeneration
YesPURPOSE. To compare microperimetric sensitivity around the monocular preferred retinal
locus (mPRL) in age-related macular degeneration (AMD) to normative data, and to describe
the characteristics of visual field defects around the mPRL in AMD.
METHODS. Participants with AMD (total n ¼ 185) were either prospectively recruited (n ¼
135) or retrospectively reviewed from an existing database (n ¼ 50). Participants underwent
microperimetry using a test pattern (37 point, 58 radius) centered on their mPRL. Sensitivities
were compared to normative data by spatial interpolation, and conventional perimetric
indices were calculated. The location of the mPRL relative to the fovea and to visual field
defects was also investigated.
RESULTS. Location of mPRL varied approximately 158 horizontally and vertically. Visual field
loss within 58 of the mPRL was considerable in the majority of participants (median mean
deviation 14.7 dB, interquartile range [IQR] 19.6 to 9.6 dB, median pattern standard
deviation 7.1 dB [IQR 4.8–9.0 dB]). Over 95% of participants had mean total deviation worse
than 2 dB across all tested locations and similarly within 18 of their mPRL. A common
pattern of placing the mPRL just foveal to a region of normal pattern deviation was found in
78% of participants. Total deviation was outside normal limits in this region in 68%.
CONCLUSIONS. Despite altering fixation to improve vision, people with AMD exhibit
considerable visual field loss at and around their mPRL. The location of the mPRL was
typically just foveal to, but not within, a region of relatively normal sensitivity for the
individual, suggesting that a combination of factors drives mPRL selection.This report presents independent research funded by the NIH
The geometry of spontaneous spiking in neuronal networks
The mathematical theory of pattern formation in electrically coupled networks
of excitable neurons forced by small noise is presented in this work. Using the
Freidlin-Wentzell large deviation theory for randomly perturbed dynamical
systems and the elements of the algebraic graph theory, we identify and analyze
the main regimes in the network dynamics in terms of the key control
parameters: excitability, coupling strength, and network topology. The analysis
reveals the geometry of spontaneous dynamics in electrically coupled network.
Specifically, we show that the location of the minima of a certain continuous
function on the surface of the unit n-cube encodes the most likely activity
patterns generated by the network. By studying how the minima of this function
evolve under the variation of the coupling strength, we describe the principal
transformations in the network dynamics. The minimization problem is also used
for the quantitative description of the main dynamical regimes and transitions
between them. In particular, for the weak and strong coupling regimes, we
present asymptotic formulas for the network activity rate as a function of the
coupling strength and the degree of the network. The variational analysis is
complemented by the stability analysis of the synchronous state in the strong
coupling regime. The stability estimates reveal the contribution of the network
connectivity and the properties of the cycle subspace associated with the graph
of the network to its synchronization properties. This work is motivated by the
experimental and modeling studies of the ensemble of neurons in the Locus
Coeruleus, a nucleus in the brainstem involved in the regulation of cognitive
performance and behavior
Errors in device localization in MRI using Z-frames.
The use of a passive MRI-visible tracking frame is a common method of localizing devices in MRI space for MRI-guided procedures. One of the most common tracking frame designs found in the literature is the z-frame, as it allows six degree-of-freedom pose estimation using only a single image slice. Despite the popularity of this design, it is susceptible to errors in pose estimation due to various image distortion mechanisms in MRI. In this paper, the absolute error in using a z-frame to localize a tool in MRI is quantified over various positions of the z-frame relative to the MRI isocenter, and for various levels of static magnetic field inhomogeneity. It was found that the error increases rapidly with distance from the isocenter in both the horizontal and vertical directions, but the error is much less sensitive to position when multiple contiguous slices are used with slice-select gradient nonlinearity correction enabled, as opposed to the more common approach of only using a single image slice. In addition, the error is found to increase rapidly with an increasing level of static field inhomogeneity, even with the z-frame placed within 10 cm of the isocenter
Observing Long Colour Flux Tubes in SU(2) Lattice Gauge Theory
We present results of a high statistics study of the chromo field
distribution between static quarks in SU(2) gauge theory on lattices of volumes
16^4, 32^4, and 48^3*64, with physical extent ranging from 1.3 fm up to 2.7 fm
at beta=2.5, beta=2.635, and beta=2.74. We establish string formation over
physical distances as large as 2 fm. The results are tested against Michael's
sum rules. A detailed investigation of the transverse action and energy flux
tube profiles is provided. As a by-product, we obtain the static lattice
potential in unpreceded accuracy.Comment: 66 pages, 29 figures, uuencoded latex file with epsfigures (450 K),
supplementary full colour figures are available via ftp, CERN-TH.7413/94
(extended version
Effect of Hadron Dynamics on the Proton Lifetime
A detailed, quantitative re-examination of the effect of hadron dynamics on
baryon decay, modeled in terms of Skyrme-field tunneling, indicates that any
hadronic suppression should be quite mild. This appears to be another
illustration of the `Cheshire-cat' phenomenon, that variation of the
apportionment between description of the nucleon as a bag of quarks and
description as a Skyrme field configuration has little influence on many
nucleon properties. Perhaps the largest remaining uncertainty in evaluating the
decay rate has to do with the overlap between a specified quark-antiquark
configuration and a final meson state.Comment: minor corrections, 19 pages, 9 figure
Dimerization of inositol monophosphatase Mycobacterium tuberculosis SuhB is not constitutive, but induced by binding of the activator Mg2+
Background The cell wall of Mycobacterium tuberculosis contains a wide range of phosphatidyl inositol-based glycolipids that play critical structural roles and, in part, govern pathogen-host interactions. Synthesis of phosphatidyl inositol is dependent on free myo-inositol, generated through dephosphorylation of myo-inositol-1-phosphate by inositol monophosphatase (IMPase). Human IMPase, the putative target of lithium therapy, has been studied extensively, but the function of four IMPase-like genes in M. tuberculosis is unclear. Results We determined the crystal structure, to 2.6 Å resolution, of the IMPase M. tuberculosis SuhB in the apo form, and analysed self-assembly by analytical ultracentrifugation. Contrary to the paradigm of constitutive dimerization of IMPases, SuhB is predominantly monomeric in the absence of the physiological activator Mg2+, in spite of a conserved fold and apparent dimerization in the crystal. However, Mg2+ concentrations that result in enzymatic activation of SuhB decisively promote dimerization, with the inhibitor Li+ amplifying the effect of Mg2+, but failing to induce dimerization on its own. Conclusion The correlation of Mg2+-driven enzymatic activity with dimerization suggests that catalytic activity is linked to the dimer form. Current models of lithium inhibition of IMPases posit that Li+ competes for one of three catalytic Mg2+ sites in the active site, stabilized by a mobile loop at the dimer interface. Our data suggest that Mg2+/Li+-induced ordering of this loop may promote dimerization by expanding the dimer interface of SuhB. The dynamic nature of the monomer-dimer equilibrium may also explain the extended concentration range over which Mg2+ maintains SuhB activity
The Nuclear Sigma Term in the Skyrme Model: Pion-Nucleus Interaction
The nuclear sigma term is calculated including the nuclear matrix element of
the derivative of the NN interaction with respect to the quark mass,
. The NN potential is evaluated in the
skyrmion-skyrmion picture within the quantized product ansatz. The contribution
of the NN potential to the nuclear sigma term provides repulsion to the
pion-nucleus interaction. The strength of the s-wave pion-nucleus optical
potential is estimated including such contribution. The results are consistent
with the analysis of the experimental data.Comment: 16 pages (latex), 3 figures (eps), e-mail: [email protected] and
[email protected]
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