Giant Enhancement of Surface Second Harmonic Generation in BaTiO_3 due to Photorefractive Surface Wave Excitation

We report observation of strongly enhanced surface SHG in BaTiO_3 due to excitation of a photorefractive surface electromagnetic wave. Surface SH intensity may reach 10^{-2} of the incident fundamental light intensity. Angular, crystal orientation and polarization dependencies of this SHG are presented. Possible applications of this effect in nonlinear surface spectroscopy are discussed.Comment: 5 pages, 6 figures, submitted to Physical Review Letters on the 3/29/199

Capillary electrophoretic separation of nanoparticles

In the present work, CdSe nanocrystals (NCs) synthesized with a trioctylphosphine surface passivation layer were modified using amphiphilic molecules to form a surface bilayer capable of providing stable NCs aqueous solutions. Such modified nanocrystals were used as a test solute in order to analyze new electrophoretic phenomena, by applying a micellar plug as a separation tool for discriminating nanocrystals between micellar and micelle-free zones during electrophoresis. The distribution of NCs between both zones depended on the affinity of nanocrystals towards the micellar zone, and this relies on the kind of surface ligands attached to the NCs, as well as electrophoretic conditions applied. In this case, the NCs that migrated within a micellar zone can be focused using a preconcentration mechanism. By modifying electrophoretic conditions, NCs were forced to migrate outside the micellar zone in the form of a typical CZE peak. In this situation, a two-order difference in separation efficiencies, in terms of theoretical plates, was observed between focused NCs (N ~ 107) and a typical CZE peak for NCs (N ~ 105). By applying the amino-functionalized NCs the preconcentration of NCs, using a micellar plug, was examined, with the conclusion that preconcentration efficiency, in terms of the enhancement factor for peak height (SEFheight) can be, at least 20. The distribution effect was applied to separate CdSe/ZnS NCs encapsulated in silica, as well as surface-modified with DNA, which allows the estimation of the yield of conjugation of biologically active molecules to a particle surface

Transcriptional Responses of Arabidopsis thaliana during Wilt Disease Caused by the Soil-Borne Phytopathogenic Bacterium, Ralstonia solanacearum

Bacterial wilt is a common disease that causes severe yield and quality losses in many plants. In the present study, we used the model Ralstonia solanacearum-Arabidopsis thaliana pathosystem to study transcriptional changes associated with wilt disease development. Susceptible Col-5 plants and RRS1-R-containing resistant Nd-1 plants were root-inoculated with R. solanacearum strains harbouring or lacking the matching PopP2 avirulence gene. Gene expression was marginally affected in leaves during the early stages of infection. Major changes in transcript levels took place between 4 and 5 days after pathogen inoculation, at the onset of appearance of wilt symptoms. Up-regulated genes in diseased plants included ABA-, senescence- and basal resistance-associated genes. The influence of the plant genetic background on disease-associated gene expression is weak although some genes appeared to be specifically up-regulated in Nd-1 plants. Inactivation of some disease-associated genes led to alterations in the plant responses to a virulent strain of the pathogen. In contrast to other pathosystems, very little overlap in gene expression was detected between the early phases of the resistance response and the late stages of disease development. This observation may be explained by the fact that above-ground tissues were sampled for profiling whereas the bacteria were applied to root tissues