3,937 research outputs found
Modification of anatase TiO(001) surface electronic structure by Au impurity
We have used density functional theory calculations based on the projector
augmented wave method to investigate the electronic structure of
Au-incorporated anatase TiO(001) surface. Due to the coordination with
several level oxygens, Au atoms can be encapsulated inside TiO slab. Au is
adsorbed over the surface Ti--O bond, so called the bridge site on anatase
TiO(001)--11 surface. However, for 0.25 ML coverage, Au atoms
energetically prefer to stay at 0.64 {\AA} above the midpoint of the two
surface oxygens which is significantly closer to the surface layer. When
implanted inside the slab for full coverage, Au forms parallel metallic wires
inside TiO lattice where interlayer distances increase due to local
segregation. Au brings half-filled impurity states into the band gap leading to
metallization, in addition to other filled surface and impurity bands within
the gap. These Au-driven Fermi-level-pinning gap states are close to, or even
in some cases inside, the conduction band of the host slab. On the other hand,
if Au is substituted for the surface Ti atom, Fermi level falls lower in the
gap closer to the valence band top.Comment: 10 pages, 4 figure
A study of Mg adsorption on Si(001) surface from first principles
First-principles calculations using density functional theory based on
norm-conserving pseudopotentials have been performed to investigate the Mg
adsorption on the Si(001) surface for 1/4, 1/2 and 1 monolayer coverages. For
both 1/4 and 1/2 ML coverages it has been found that the most favorable site
for the Mg adsorption is the cave site between two dimer rows consistent with
the recent experiments. For the 1 ML coverage we have found that the most
preferable configuration is when both Mg atoms on 2x1 reconstruction occupy the
two shallow sites. We have found that the minimum energy configurations for 1/4
ML coverage is a 2x2 reconstruction while for the 1/2 and 1 ML coverages they
are 2x1.Comment: 7 pages, 4 figure
Re-assigning (1x2) reconstruction of rutile TiO_2(110) from DFT+U calculations
Physically reasonable electronic structures of reconstructed rutile
TiO_2(110)-(1x2) surfaces were studied using density functional theory (DFT)
supplemented with Hubbard U on-site Coulomb repulsion acting on the d
electrons, so called as the DFT+U approach. Two leading reconstruction models
proposed by Onishi--Iwasawa and Park et al. were compared in terms of their
thermodynamic stabilities.Comment: 4 pages, 4 figures, 2 table
Cs adsorption on Si(001) surface: ab initio study
First-principles calculations using density functional theory based on
norm-conserving pseudopotentials have been performed to investigate the Cs
adsorption on the Si(001) surface for 0.5 and 1 ML coverages. We found that the
saturation coverage corresponds to 1 ML adsorption with two Cs atoms occupying
the double layer model sites. While the 0.5 ML covered surface is of metallic
nature, we found that 1 ML of Cs adsorption corresponds to saturation coverage
and leads to a semiconducting surface. The results for the electronic behavior
and surface work function suggest that adsorption of Cs takes place via
polarized covalent bonding.Comment: 8 pages, 7 figure
Strong Electron-Hole Exchange in Coherently Coupled Quantum Dots
We have investigated few-body states in vertically stacked quantum dots. Due
to small inter-dot tunneling rate, the coupling in our system is in a
previously unexplored regime where electron-hole exchange is the dominant spin
interaction. By tuning the gate bias, we are able to turn this coupling off and
study a complementary regime where total electron spin is a good quantum
number. The use of differential transmission allows us to obtain unambiguous
signatures of the interplay between electron and hole spin interactions. Small
tunnel coupling also enables us to demonstrate all-optical charge sensing,
where conditional exciton energy shift in one dot identifies the charging state
of the coupled partner.Comment: 10 pages, 3 figure
Electronic Structure of a Chain-like Compound: TlSe
An ab-initio pseudopotential calculation using density functional theory
within the local density approximation has been performed to investigate the
electronic properties of TlSe which is of chain-like crystal geometry. The
energy bands and effective masses along high symmetry directions, the density
of states and valence charge density distributions cut through various planes
are presented. The results have been discussed in terms of previously existing
experimental and theoretical data, and comparisons with similar compounds have
been made.Comment: 7 page
DFT study of noble metal impurities of TiO2(110)
Cataloged from PDF version of article.Atomic and electronic structures of TiO2(110) surface with possible adsorptional, substitutional and interstitial Au or Pt elemental impurities at full and one-sixth monolayer concentrations were investigated by density functional theory calculations using the projector augmented wave approach within the plane wave method. Relative thermodynamic stabilities of such phases have been discussed by means of their surface free energies. Our results suggest that tunable photocatalytic activity can be achieved on Pt atom admixed rutile (110) surface at low coverages
Disease associated with equine coronavirus infection and high case fatality rate.
BackgroundEquine coronavirus (ECoV) is associated with clinical disease in adult horses. Outbreaks are associated with a low case fatality rate and a small number of animals with signs of encephalopathic disease are described.ObjectivesThe aim of this study is to describe the epidemiological and clinical features of two outbreaks of ECoV infection that were associated with an high case fatality rate.Animals14 miniature horses and 1 miniature donkey testing fecal positive for ECoV from two related disease outbreaks.MethodsRetrospective study describing the epidemiological findings, clinicopathological findings, and fecal viral load from affected horses.ResultsIn EcoV positive horses, 27% (4/15) of the animals died or were euthanized. Severe hyperammonemia (677 μmol/L, reference range ≤ 60 μmol/L) was identified in one animal with signs of encephalopathic disease that subsequently died. Fecal viral load (ECoV genome equivalents per gram of feces) was significantly higher in the nonsurvivors compared to animals that survived (P = .02).Conclusions and clinical importanceEquine coronavirus had a higher case fatality rate in this group of miniature horses than previously reported in other outbreaks of varying breeds. Hyperammonemia could contribute to signs of encephalopathic disease, and the fecal viral load might be of prognostic value in affected horses
Project PROMETHEUS: Design and Construction of a Radio Frequency Quadrupole at TAEK
The PROMETHEUS Project is ongoing for the design and development of a 4-vane
radio frequency quadrupole (RFQ) together with its H+ ion source, a low energy
beam transport (LEBT) line and diagnostics section. The main goal of the
project is to achieve the acceleration of the low energy ions up to 1.5 MeV by
an RFQ (352 MHz) shorter than 2 meter. A plasma ion source is being developed
to produce a 20 keV, 1 mA H+ beam. Simulation results for ion source,
transmission and beam dynamics are presented together with analytical studies
performed with newly developed RFQ design code DEMIRCI. Simulation results
shows that a beam transmission 99% could be achieved at 1.7 m downstream
reaching an energy of 1.5 MeV. As the first phase an Aluminum RFQ prototype,
the so-called cold model, will be built for low power RF characterization. In
this contribution the status of the project, design considerations, simulation
results, the various diagnostics techniques and RFQ manufacturing issues are
discussed.Comment: 4 pages, 8 figures, Proceedings of the 2nd International Beam
Instrumentation Conference 2013 (IBIC'13), 16-19 Sep 2013, WEPC02, p. 65
- …