523 research outputs found
The Spatial Properties of L- and M-Cone Inputs to Electroretinograms That Reflect Different Types of Post-Receptoral Processing
yesWe studied the spatial arrangement of L- and M-cone driven electroretinograms (ERGs) reflecting
the activity of magno- and parvocellular pathways. L- and M-cone isolating sine
wave stimuli were created with a four primary LED stimulator using triple silent substitution
paradigms. Temporal frequencies were 8 and 12 Hz, to reflect cone opponent activity, and
30, 36 and 48 Hz to reflect luminance activity. The responses were measured for full-field
stimuli and for different circular and annular stimuli. The ERG data confirm the presence of
two different mechanisms at intermediate and high temporal frequencies. The responses
measured at high temporal frequencies strongly depended upon spatial stimulus configuration.
In the full-field conditions, the L-cone driven responses were substantially larger than
the full-field M-cone driven responses and also than the L-cone driven responses with
smaller stimuli. The M-cone driven responses at full-field and with 70° diameter stimuli displayed
similar amplitudes. The L- and M-cone driven responses measured at 8 and 12 Hz
were of similar amplitude and approximately in counter-phase. The amplitudes were constant
for most stimulus configurations. The results indicate that, when the ERG reflects luminance
activity, it is positively correlated with stimulus size. Beyond 35° retinal eccentricity,
the retina mainly contains L-cones. Small stimuli are sufficient to obtain maximal ERGs at
low temporal frequencies where the ERGs are also sensitive to cone-opponent processin
Ab initio calculations for bromine adlayers on the Ag(100) and Au(100) surfaces: the c(2x2) structure
Ab initio total-energy density-functional methods with supercell models have
been employed to calculate the c(2x2) structure of the Br-adsorbed Ag(100) and
Au(100) surfaces. The atomic geometries of the surfaces and the preferred
bonding sites of the bromine have been determined. The bonding character of
bromine with the substrates has also been studied by analyzing the electronic
density of states and the charge transfer. The calculations show that while the
four-fold hollow-site configuration is more stable than the two-fold
bridge-site topology on the Ag(100) surface, bromine prefers the bridge site on
the Au(100) surface. The one-fold on-top configuration is the least stable
configuration on both surfaces. It is also observed that the second layer of
the Ag substrate undergoes a small buckling as a consequence of the adsorption
of Br. Our results provide a theoretical explanation for the experimental
observations that the adsorption of bromine on the Ag(100) and Au(100) surfaces
results in different bonding configurations.Comment: 10 pages, 4 figure, 5 tables, Phys. Rev. B, in pres
Comparison of the reliability of multifocal visual evoked cortical potentials generated by pattern reversal and pattern pulse stimulation
This study compared the effectiveness of the multifocal visual evoked cortical potentials (mfVEP) elicited by pattern pulse stimulation with that of pattern reversal in producing reliable responses (signal-to-noise ratio >1.359). Participants were 14 healthy subjects. Visual stimulation was obtained using a 60-sector dartboard display consisting of 6 concentric rings presented in either pulse or reversal mode. Each sector, consisting of 16 checks at 99% Michelson contrast and 80 cd/m² mean luminance, was controlled by a binary m-sequence in the time domain. The signal-to-noise ratio was generally larger in the pattern reversal than in the pattern pulse mode. The number of reliable responses was similar in the central sectors for the two stimulation modes. At the periphery, pattern reversal showed a larger number of reliable responses. Pattern pulse stimuli performed similarly to pattern reversal stimuli to generate reliable waveforms in R1 and R2. The advantage of using both protocols to study mfVEP responses is their complementarity: in some patients, reliable waveforms in specific sectors may be obtained with only one of the two methods. The joint analysis of pattern reversal and pattern pulse stimuli increased the rate of reliability for central sectors by 7.14% in R1, 5.35% in R2, 4.76% in R3, 3.57% in R4, 2.97% in R5, and 1.78% in R6. From R1 to R4 the reliability to generate mfVEPs was above 70% when using both protocols. Thus, for a very high reliability and thorough examination of visual performance, it is recommended to use both stimulation protocols
Excluded Volume Effects in the Quark Meson Coupling Model
Excluded volume effects are incorporated in the quark meson coupling model to
take into account in a phenomenological way the hard core repulsion of the
nuclear force. The formalism employed is thermodynamically consistent and does
not violate causality. The effects of the excluded volume on in-medium nucleon
properties and the nuclear matter equation of state are investigated as a
function of the size of the hard core. It is found that in-medium nucleon
properties are not altered significantly by the excluded volume, even for large
hard core radii, and the equation of state becomes stiffer as the size of the
hard core increases.Comment: 14 pages, revtex, 6 figure
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS
We present the results of a search for new, heavy particles that decay at a
significant distance from their production point into a final state containing
charged hadrons in association with a high-momentum muon. The search is
conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV
and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS
detector operating at the Large Hadron Collider. Production of such particles
is expected in various scenarios of physics beyond the standard model. We
observe no signal and place limits on the production cross-section of
supersymmetric particles in an R-parity-violating scenario as a function of the
neutralino lifetime. Limits are presented for different squark and neutralino
masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final
version to appear in Physics Letters
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