Modification of anatase TiO2_2(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$_2$(001) surface. Due to the coordination with several level oxygens, Au atoms can be encapsulated inside TiO$_2$ slab. Au is adsorbed over the surface Ti--O bond, so called the bridge site on anatase TiO$_2$(001)--1$\times$1 surface. However, for 0.25 ML coverage, Au atoms energetically prefer to stay at 0.64 {\AA} above the midpoint of the two surface oxygens which is significantly closer to the surface layer. When implanted inside the slab for full coverage, Au forms parallel metallic wires inside TiO$_2$ 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

Antioxidant Enzyme Activities and Abiotic Stress Tolerance Relationship in Vegetable Crops

Climatic changes can cause serious reductions in yield and crop quality. Under the threat of climatic changes, one of the precautions to cope is selection and development of resistant vegetable genotypes to abiotic stresses. Several physiological and biochemical reactions and different tolerance levels can occur according to plant species. When plants are subjected to environmental stresses such as salinity, drought, temperature extremes, herbicide treatment and mineral deficiency, the balance between the production of reactive oxygen species (ROS) and the quenching activity of antioxidants is upset, often resulting in oxidative damage. Since activated oxygen species can disrupt normal metabolism through oxidative damage to lipids, protein and nucleic acids, plants possess a number of antioxidant enzymes that protect them from these cytotoxic effects. To control the level of ROS and to protect cells under stress conditions, plant tissues contain several enzymes for scavenging ROS. The high levels of antioxidative enzyme activities were determined in the tolerant genotypes of tomatoes, eggplant, peppers, cucumbers, melons, squash, beans, okra, etc. to several abiotic stress factors. Both the whole plant and in vitro callus culture experiments gave similar results. Antioxidant enzymes can be useful for screening to determine the tolerant and sensitive plant genotypes against abiotic stresses

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

Ab-initio study of BaTiO3 surfaces

We have carried out first-principles total-energy calculations of (001) surfaces of the tetragonal and cubic phases of BaTiO3. Both BaO-terminated (type I) and TiO2-terminated (type II) surfaces are considered, and the atomic configurations have been fully relaxed. We found no deep-gap surface states for any of the surfaces, in agreement with previous theoretical studies. However, the gap is reduced for the type-II surface, especially in the cubic phase. The surface relaxation energies are found to be substantial, i.e., many times larger than the bulk ferroelectric well depth. Nevertheless, the influence of the surface upon the ferroelectric order parameter is modest; we find only a small enhancement of the ferroelectricity near the surface.Comment: 8 pages, two-column style with 4 postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/index.html#pad_sur

Accurate evaluation of the interstitial KKR-Green function

It is shown that the Brillouin zone integral for the interstitial KKR-Green function can be evaluated accurately by taking proper care of the free-electron singularities in the integrand. The proposed method combines two recently developed methods, a supermatrix method and a subtraction method. This combination appears to provide a major improvement compared with an earlier proposal based on the subtraction method only. By this the barrier preventing the study of important interstitial-like defects, such as an electromigrating atom halfway along its jump path, can be considered as being razed.Comment: 23 pages, RevTe

Effects of salt stress on ion accumulation and activity of some antioxidant enzymes in melon (Cucumis melo L.)

The changes in ion acumulation and the possible involvement of the antioxidant system in relation to the tolerance of salt stress was investigated in melon (Cucumis melo L.). Four local Turkish varieties (Besni, Midyat, Yuva and Şemame), three cultivars (Ananas, Galia C8 and Galia F1) and C. melo var. flexuosus were grown in hydroponic culture. The 4-5 true leaf stages of melon seedlings were subjected to 100 mM NaCl for 8 days. In Galia C8 and Galia F1 cultivars and Midyat and Besni varieties level of Cl ion accumulation was lower, but activities of superoxide dismutase (SOD; EC 1.15.1.1) and catalase (CAT; EC 1.11.1.6) were inherently higher than in Ananas, Yuva and C. flexuosus. These results possibly suggest that 'Galia C8' and 'Galia F1' exhibit a better protection mechanism against oxidative damage by maintaining a higher inherited and induced activity of antioxidant enzymes than the relatively sensitive plants of the melon

Induction of symmetrical nucleus division and multi-nucleate structures in microspores of eggplant (Solanum melongena L.) cultured in vitro [Indução de divisão nuclear simétrica e estruturas multinucleadas em micrósporos de berinjela (Solanum melongena L.) cultivados in vitro]

A modification of a protocol used to induce tobacco microspore embryogenesis was tested in eggplant (Solanum melongena L.). In tobacco, uninucleate microspores are subjected to stress treatment by culturing in mannitol containing "B" medium at 33°C for six days. The microspores are then transferred to maltose containing AT3 medium for further development. In the experiment presented here late uninucleate and bi-nucleate microspores of the eggplant cultivar Bambino were pre-cultured in B medium and then incubated at +4°C, 25°C and 33°C, respectively, for two days. After the pre-treatments, microspore cultures were transferred to AT3 medium containing 0.25 M maltose and maintained at 25°C in the dark. Presence of symmetrical division and multinucleate structures was checked with DAPI staining of the nucleus after one and two weeks. Symmetrical division of the nucleus and multinucleate structures were observed only in uni-nucleate microspores pre-treated at 33°C for two days. The frequency of multinucleate structures was 19.4% under these conditions. We demonstrated that eggplant is responsive to the modified tobacco protocol in the production of symmetrically division and multinucleate structures. These results may be used as a basis for adaptation fully of the tobacco system in eggplant

ELASTIC COEFFICIENTS IN TLGA(S1-XSEX)2 AND TLINXGA1-XS2 LAYER MIXED-CRYSTALS BY BRILLOUIN-SCATTERING

The compositional variation of the elastic coefficients C-11 and C33 for TlGa(S1-xSex) and TlInxGa1-xS2 layer mixed crystals are discussed using Brillouin scattering measurements. Clear anomalies are observed for the longitudinal phonons propagating parallel to the (00 1) plane (elastic coefficient C-11) at x(c) congruent-to 0.8 and x(c) congruent-to 0.3 in TlInxGa1-xS2 and TlGa(S1-xSex)2, respectively. These anomalies are explained by the formation of infinite clusters. A considerable difference in the rate of change of the elastic coefficient C33 with the composition for the mixed crystals TlGa(S1-xSex)2 and TlInxGa1-xS2 is observed. The temperature variation of C33 for a TlIn0.95Ga0.05S2 mixed crystals is also given and the results are discussed

Structural, electronic and vibrational properties of ordered intermetallic alloys CoZ (Z=Al, Be, Sc and Zr) from first-principles total-energy calculations

WOS: 000323633100003Self-consistent band calculations on four intermetallic compounds of the CsCl structure are presented. The calculations were performed employing the self-consistent ultrasoft pseudopotential method based on the density functional theory, within the local density approximation and the generalized gradient approximation. The calculations predicted that the equilibrium lattice constants are in excellent agreement with the experiment for CoAl and are 1% smaller than experimental values for CoBe, CoSc and CoZr, respectively. In the present study, ordered CoAl do not show any magnetic moment, whereas the other three compounds have moderate magnetic moments of about 0.2 and 0.7 Bohr magnetons ((B) ) per atom. The elastic constants are calculated using two approaches, the energy-strain method and the use of phonon dispersion curves. The values obtained from the two methods are in reasonable agreement for the studied intermetallic compounds CoZ (Z=Al, Be, Sc and Zr). The brittleness and ductility properties of CoZ (Z=Al, Be, Sc and Zr) are determined by Poisson's ratio sigma criterion and Pugh's criterion. The calculated elastic constants satisfy the mechanical stability criterion and the ductility of CoZr and CoSc is predicted by Pugh's criterion. The band structure and density of states, and phonon dispersion curves have been obtained and compared with the available experimental results as well as with existing theoretical calculations. We studied and discussed the position of Fermi level for the selected four intermetallic compounds.Gazi University Research Project UnitGazi University [05/2012-07, 05/2012-08, 05/2012-62, 05/2012-63]; Hacettepe University Research Project UnitHacettepe University [0701602005]This work was supported by the Gazi University Research Project Unit under Project No 05/2012-07, 05/2012-08, 05/2012-62, 05/2012-63 and Hacettepe University Research Project Unit under Project No 0701602005