2,446 research outputs found
Correlations between the interfacial chemistry and current-voltage behavior of n-GaAs/liquid junctions
Correlations between the surface chemistry of etched, (100) oriented n-GaAs electrodes and their subsequent photoelectrochemical behavior have been probed by high-resolution x-ray photoelectron spectroscopy. GaAs photoanodes were chemically treated to prepare either an oxide-free near stoichiometric surface, a surface enriched in zero-valent arsenic (As0), or a substrate-oxide terminated surface. The current-voltage (I-V) behavior of each surface type was subsequently monitored in contact with several electrolytes
Estimating Parasitism of Colorado Potato Beetle Eggs, \u3ci\u3eLeptinotarsa Decemlineata\u3c/i\u3e (Coleoptera: Chrysomelidae), by \u3ci\u3eEdovum Puttleri\u3c/i\u3e (Hymenoptera: Eulophidae)
A computer simulation was used to evaluate methods for estimating parasitism of Colorado potato beetle egg mass populations by Edovum puttleri. The algorithm incorporated the specific attack behavior of E. puttleri, and a development time for parasitized egg masses of ca. 2.9 times that of healthy egg masses. Of the methods compared, a modification of Southwood\u27s graphical technique was found to be most accurate in relation to the true parasitism derived from the algorithm. A regression equation is presented to correct the error in this method at high levels of parasitism. A second simulation was used to test the accuracy of this correcter where in a jacknife procedure was used to generate a mean and variance for estimates of parasitism
Indirect tests of the Randall-Sundrum model
I present phenomenological implications of the Randall-Sundrum model for
indirect searches, specifically a selection of flavor observables and
Higgs-related collider searches. I review the interplay of constraints from CP
violation in flavor physics, possible effects in rare decays, and
model-specific protection mechanisms. Deviations in the Higgs couplings to
fermions and, at one-loop, to gluons are unexpectedly strong and lead to strong
modifications in Higgs searches.Comment: 8 pages, 6 figures; Talk given at Discrete '10: Symposium on
Prospects in the Physics of Discrete Symmetries, Rome, Italy, 6-11 Dec 201
Functional Organization of Visual Cortex in the Owl Monkey
In this study, we compared the organization of orientation preference in visual areas V1, V2, and V3. Within these visual areas, we also
quantified the relationship between orientation preference and cytochrome oxidase (CO) staining patterns. V1 maps of orientation
preference contained both pinwheels and linear zones. The location of CO blobs did not relate in a systematic way to maps of orientation;
although, as in other primates, there were approximately twice as many pinwheels as CO blobs. V2 contained bands of high and low
orientation selectivity. The bands of high orientation selectivity were organized into pinwheels and linear zones, but iso-orientation
domains were twice as large as those in V1. Quantitative comparisons between bands containing high or low orientation selectivity and
CO dark and light bands suggested that at least four functional compartments exist in V2, CO dense bands with either high or low
orientation selectivity, and CO light bands with either high or low selectivity. We also demonstrated that two functional compartments
exist in V3, with zones of high orientation selectivity corresponding to CO dense areas and zones of low orientation selectivity corresponding
to CO pale areas. Together with previous findings, these results suggest that the modular organization of V1 is similar across
primates and indeed across most mammals. V2 organization in owl monkeys also appears similar to that of other simians but different
from that of prosimians and other mammals. Finally, V3 of owl monkeys shows a compartmental organization for orientation selectivity
that remains to be demonstrated in other primates
Testing Asteroseismic Radii of Dwarfs and Subgiants with Kepler and Gaia
We test asteroseismic radii of Kepler main-sequence and subgiant stars by
deriving their parallaxes which are compared with those of the first Gaia data
release. We compute radii based on the asteroseismic scaling relations as well
as by fitting observed oscillation frequencies to stellar models for a subset
of the sample, and test the impact of using effective temperatures from either
spectroscopy or the infrared flux method. An offset of 3%, showing no
dependency on any stellar parameters, is found between seismic parallaxes
derived from frequency modelling and those from Gaia. For parallaxes based on
radii from the scaling relations, a smaller offset is found on average;
however, the offset becomes temperature dependent which we interpret as
problems with the scaling relations at high stellar temperatures. Using the
hotter infrared flux method temperature scale, there is no indication that
radii from the scaling relations are inaccurate by more than about 5%. Taking
the radii and masses from the modelling of individual frequencies as reference
values, we seek to correct the scaling relations for the observed temperature
trend. This analysis indicates that the scaling relations systematically
overestimate radii and masses at high temperatures, and that they are accurate
to within 5% in radius and 13% in mass for main-sequence stars with
temperatures below 6400 K. However, further analysis is required to test the
validity of the corrections on a star-by-star basis and for more evolved stars.Comment: 12 pages, 9 figures. Accepted for publication in MNRA
Impacts of a flaring star-forming disc and stellar radial mixing on the vertical metallicity gradient
Using idealized N-body simulations of a Milky Way-sized disc galaxy, we qualitatively study how the metallicity distributions of the thin disc star particles are modified by the formation of the bar and spiral arm structures. The thin disc in our numerical experiments initially has a tight negative radial metallicity gradient and a constant vertical scaleheight. We show that the radial mixing of stars drives a positive vertical metallicity gradient in the thin disc. On the other hand, if the initial thin disc is flared, with vertical scaleheight increasing with galactocentric radius, the metal-poor stars, originally in the outer disc, become dominant in regions above the disc plane at every radii. This process can drive a negative vertical metallicity gradient, which is consistent with the current observed trend. This model mimics a scenario where the star-forming thin disc was flared in the outer region at earlier epochs. Our numerical experiment with an initial flared disc predicts that the negative vertical metallicity gradient of the mono-age relatively young thin disc population should be steeper in the inner disc, and the radial metallicity gradient of the mono-age population should be shallower at greater heights above the disc plane. We also predict that the metallicity distribution function of mono-age young thin disc populations above the disc plane would be more positively skewed in the inner disc compared to the outer disc
Solvable model of a strongly-driven micromaser
We study the dynamics of a micromaser where the pumping atoms are strongly
driven by a resonant classical field during their transit through the cavity
mode. We derive a master equation for this strongly-driven micromaser,
involving the contributions of the unitary atom-field interactions and the
dissipative effects of a thermal bath. We find analytical solutions for the
temporal evolution and the steady-state of this system by means of phase-space
techniques, providing an unusual solvable model of an open quantum system,
including pumping and decoherence. We derive closed expressions for all
relevant expectation values, describing the statistics of the cavity field and
the detected atomic levels. The transient regime shows the build-up of mixtures
of mesoscopic fields evolving towards a superpoissonian steady-state field
that, nevertheless, yields atomic correlations that exhibit stronger
nonclassical features than the conventional micromaser.Comment: 9 pages, 16 figures. Submitted for publicatio
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