4,132 research outputs found
Improving the performance of inorganic-organic hybrid photovoltaic devices by uniform ordering of ZnO nanorods and near-atmospheric pressure nitrogen plasma treatment
Polarization-dependence of palladium deposition on ferroelectric lithium niobate (0001) surfaces
We investigate the effect of ferroelectric polarization direction on the
geometric properties of Pd deposited on the positive and negative surfaces of
LiNbO (0001). We predict preferred geometries and diffusion properties of
small Pd clusters using density functional theory, and use these calculations
as the basis for kinetic Monte Carlo simulations of Pd deposition on a larger
scale. Our results show that on the positive surface, Pd atoms favor a
clustered configuration, while on the negative surface, Pd atoms are adsorbed
in a more dispersed pattern due to suppression of diffusion and agglomeration.
This suggests that the effect of LiNbO polarization direction on the
catalytic activity of Pd [J. Phys. Chem. \textbf{88}, 1148 (1984)] is due, at
least in part, to differences in adsorption geometry. Further investigations
using these methods can aid the search for catalysts whose activities switch
reversibly with the polarization of their ferroelectric substrates
An Examination of the Relationship Between School Climate, Self-Determined Academic Motivation, and Academic Outcomes Among Middle and High School Students
The purpose of this study was to explore connections among student perceptions of specific school climate-factors, self-determined academic motivation, and academic outcomes in a sample of middle and high school students (sixth through eleventh grade). Structural equation modeling techniques were used to identify meaningful grade specific associations within a sample of 2,463 students. The school climate factors of perceived teacher support, peer support, and school bullying emerged as the most salient school climate-based predictors of academic motivation factors. Perceived teacher support positively predicted academic competence and relatedness, whereas school bullying negatively predicted relatedness. Student academic competence, in turn, was found to negatively predict amotivation and to positively predict of GPA, after controlling for previous standardized test scores. Results were found to be consistent across grades. The implications of these findings in regards to school stakeholder practices and future research directions within the school climate and academic motivation literature bases are discussed
Comparison of clinical signs and outcomes between dogs with presumptive ischemic myelopathy and dogs with acute non compressive nucleus pulposus extrusion
Positional Coincidence between the High-latitude Steady Unidentified Gamma-ray Sources and Possibly Merging Clusters of Galaxies
We report an evidence for the first time that merging clusters of galaxies
are a promising candidate for the origin of high galactic-latitude, steady
unidentified EGRET gamma-ray sources. Instead of using past optical catalogs of
eye-selected clusters, we made a matched-filter survey of galaxy clusters over
4\arcdeg \times 4\arcdeg areas around seven steady unidentified EGRET sources
at |b|>45\arcdeg together with a 100 \sq \arcdeg area near the South
Galactic Pole as a control field. In total, 154 Abell-like cluster candidates
and 18 close pairs/groups of these clusters, expected to be possibly merging
clusters, were identified within estimated redshift . Five
among the seven EGRET sources have one or two cluster pairs/groups (CPGs)
within 1\arcdeg from them. We assess the statistical significance of this
result by several methods, and the confidence level of the real excess is
maximally 99.8% and 97.8% in a conservative method. In contrast, we found no
significant correlation with single clusters. In addition to the spatial
correlation, we also found that the richness of CPGs associated with EGRET
sources is considerably larger than those of CPGs in the control field. These
results imply that a part of the steady unidentified EGRET sources at
high-latitude are physically associated with close CPGs, not with single
clusters. We also discuss possible interpretations of these results. We argue
that, if these associations are real, they are difficult to explain by hadronic
processes, but best explained by the inverse-Compton scattering by high energy
electrons accelerated in shocks of cluster formation, as recently proposed.Comment: 9 pages, 2 PostScript figures, uses emulateapj5.sty, added new
analysis and discussion, ApJ accepte
Gamma Rays from Clusters and Groups of Galaxies: Cosmic Rays versus Dark Matter
Clusters of galaxies have not yet been detected at gamma-ray frequencies;
however, the recently launched Fermi Gamma-ray Space Telescope, formerly known
as GLAST, could provide the first detections in the near future. Clusters are
expected to emit gamma rays as a result of (1) a population of high-energy
primary and re-accelerated secondary cosmic rays (CR) fueled by structure
formation and merger shocks, active galactic nuclei and supernovae, and (2)
particle dark matter (DM) annihilation. In this paper, we ask the question of
whether the Fermi telescope will be able to discriminate between the two
emission processes. We present data-driven predictions for a large X-ray flux
limited sample of galaxy clusters and groups. We point out that the gamma ray
signals from CR and DM can be comparable. In particular, we find that poor
clusters and groups are the systems predicted to have the highest DM to CR
emission at gamma-ray energies. Based on detailed Fermi simulations, we study
observational handles that might enable us to distinguish the two emission
mechanisms, including the gamma-ray spectra, the spatial distribution of the
signal and the associated multi-wavelength emissions. We also propose optimal
hardness ratios, which will help to understand the nature of the gamma-ray
emission. Our study indicates that gamma rays from DM annihilation with a high
particle mass can be distinguished from a CR spectrum even for fairly faint
sources. Discriminating a CR spectrum from a light DM particle will be instead
much more difficult, and will require long observations and/or a bright source.
While the gamma-ray emission from our simulated clusters is extended,
determining the spatial distribution with Fermi will be a challenging task
requiring an optimal control of the backgrounds.Comment: revised to match resubmitted version, 35 pages, 16 figures: results
unchanged, some discussion added and unnecessary text and figures remove
Microoptical Realization of Arrays of Selectively Addressable Dipole Traps: A Scalable Configuration for Quantum Computation with Atomic Qubits
We experimentally demonstrate novel structures for the realisation of
registers of atomic qubits: We trap neutral atoms in one and two-dimensional
arrays of far-detuned dipole traps obtained by focusing a red-detuned laser
beam with a microfabricated array of microlenses. We are able to selectively
address individual trap sites due to their large lateral separation of 125 mu
m. We initialize and read out different internal states for the individual
sites. We also create two interleaved sets of trap arrays with adjustable
separation, as required for many proposed implementations of quantum gate
operations
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