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151.
Gustafson J Borg M Mikkelsen A Gorovikov S Lundgren E Andersen JN 《Physical review letters》2003,91(5):056102
Vicinal Rh(111) surfaces are studied with high resolution core level photoemission. We demonstrate the possibility to distinguish between the different kinds of surface atoms on these surfaces by virtue of their 3d core level binding energies. In particular, the low coordinated step atoms are found to exhibit a clear fingerprint in Rh 3d spectra. We demonstrate how this may be used to show that initial oxygen adsorption occurs on the steps and not on the terraces of the vicinal surfaces. 相似文献
152.
A. H. Sørensen A. Kühle L. Theil Hansen H. Busch L. Jin Christiansen J. Mikkelsen N. Herholdt-Rasmussen K. A. Mørch J. Bohr 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,40(1):509-512
Nanometer-sized clusters of copper have been produced in a hollow cathode sputtering source and deposited on SiOx. Halo-like structures consisting of micrometer sized protrusions in the silicon oxide surface surrounded by thin rings of smaller particles are observed. The area in between seems to be depleted of particles. We propose that the halo-like structures are a result of electrostatic forces acting between the incoming charged clusters and charged regions on the surface. A simple computer simulation supports this suggestion. 相似文献
153.
Inelastic light scattering spectra of CuI and AgI in the α and melt phases are reported and shown to involve two depolarized Lorentzian components centered at zero frequency. The narrow component is interpreted in terms of ionic motions and we propose that the observed depolarized scattering is caused by correlated configurations of the mobile ions. 相似文献
154.
Measurements of the extended X-ray absorption fine structure (EXAFS) on the Ag K-shell absorption in RbAg4I5 show that in all three crystalline phases the equilibrium position of the Ag ions is near the center of tetrahedra formed by the iodine atoms. In addition, Ag-Ag correlations, which persist into the superionic α-phase, are observed. 相似文献
155.
S.R. Jensen B.J. Nielsen C.B. Mikkelsen J.J. Hoffmann S.D. Jolad J.R. Cole 《Tetrahedron letters》1979,20(35):3261-3262
The original structure of the antitumor agent, penstemide, has been revised to an isovaleroyl type iridoid glucoside based upon additional physical data. 相似文献
156.
We show that the transition from laminar to active behavior in extended chaotic systems can vary from a continuous transition in the universality class of directed percolation with infinitely many absorbing states to what appears as a first-order transition. The latter occurs when finite lifetime nonchaotic structures, called "solitons," dominate the dynamics. We illustrate this scenario in an extension of the deterministic Chaté-Manneville coupled map lattice model and in a soliton including variant of the stochastic Domany-Kinzel cellular automaton. 相似文献
157.
Stine T. Olsen Thorsten Hansen Kurt V. Mikkelsen 《Theoretical chemistry accounts》2011,130(4-6):839-850
We present theoretical methods and computational strategies of the effects of nanoparticles on linear optical properties of molecules. We present quantum mechanical-molecular mechanics response methods for calculating electromagnetic properties of molecules interacting with nanoparticles and we report strategies for calculating electronic and redox states of molecules sandwiched between gold nanoparticles. 相似文献
158.
Elm J Lykkebo J Sørensen TJ Laursen BW Mikkelsen KV 《The journal of physical chemistry. A》2011,115(43):12025-12033
Triarylmethylium cations with the three rings linked by two bridging groups constitute a special class of [4]heterohelicenium dyes that combine high configurational stability with the optical properties of classic dye compounds. The racemization barriers and electronic circular dichroism of seven [4]heterohelicenium analogues are investigated with density functional theory to consider different design strategies. The racemization barriers are examined with the B3LYP functional utilizing the basis set 6-31+G* with respect to bridging heteroatoms in the helicenium motif and with different bulky substituents in the helix pitch. The racemization barriers of the [4]heterohelicenium are found to be highly dependent on the relative size of the bridging atom. Nucleophilic attack at the carbenium ion leads to formation of center adducts for which the racemization barriers are found to be lowered by 8-12 kJ/mol. This finding of a nucleophilic racemization catalysis may be rationalized by the loss of conjugation upon formation of an sp(3)-hybridized carbon in the center adducts. The effect of the heteroatom substitution and center adduct formation is reflected in the electronic properties of the compound calculated with the Coulomb-attenuated method CAM-B3LYP with the basis set 6-311++G**. The excitation energies are found to be highly dependent on the twisting of the helicenium framework and only weakly influenced by the electronic nature of the bridging substituent. The electronic circular dichroism is evaluated, as the rotational strength is found to be highly dependent on both the overall molecular structure and substitution pattern but with no simple correlation between structure and circular dichroism (CD) response. The calculations reveal that the magnitude of rotational strength in most cases is dominated by the angle between the electronic and magnetic transition dipole moments. Finally, it is found that computational screening of many different structures and substituents might be needed to find target structures with maximized rotational strength. 相似文献
159.
Mehdi Rahimi Hyun-Yi Youn David J. McCanna Jacob G. Sivak Susan R. Mikkelsen 《Analytical and bioanalytical chemistry》2013,405(14):4975-4979
The application of cyclic biamperometry to viability and cytotoxicity assessments of human corneal epithelial cells has been investigated. Electrochemical measurements have been compared in PBS containing 5.0 mM glucose and minimal essential growth medium. Three different lipophilic mediators including dichlorophenol indophenol, 2-methyl-1,4-naphthoquinone (also called menadione or vitamin K3) and N,N,N′,N′-tetramethyl-p-phenylenediamine have been evaluated for shuttling electrons across the cell membrane to the external medium. Transfer of these electrons to ferricyanide in the extra cellular medium results in the accumulation of ferrocyanide. The amount of ferrocyanide is then determined using cyclic biamperometry and is related to the extent of cell metabolic activity and therefore cell viability. To illustrate cytotoxicity assessment of chemicals, hydrogen peroxide, benzalkonium chloride and sodium dodecyl sulfate have been chosen as sample toxins, the cytotoxicities of which have been evaluated and compared to values reported in the literature. Similar values have been reported using colorimetric assays; however, the simplicity of this electrochemical assay can, in principle, open the way to miniaturization onto lab-on-chip devices and its incorporation into tiered-testing approaches for cytotoxicity assessment. Figure
After mediated reduction of ferricyanide by cell components, its reduced form, ferrocyanide, is quantitated using cyclic biamperometry in presence of excess ferricyanide. Concentration of ferrocyanide is then related to the extent of cell metabolic activity for viability/cytotoxicity assessments 相似文献