Browsing by Author "Sun, Qiang"

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    Cell Wall-Degrading Enzymes Enlarge the Pore Size of Intervessel Pit Membranes in Healthy and Xylella fastidiosa-Infected Grapevines
    (AMER SOC PLANT BIOLOGISTS, 2010) Perez Donoso, Alonso G.; Sun, Qiang; Roper, M. Caroline; Greve, L. Carl; Kirkpatrick, Bruce; Labavitch, John M.
    The pit membrane (PM) is a primary cell wall barrier that separates adjacent xylem water conduits, limiting the spread of xylem-localized pathogens and air embolisms from one conduit to the next. This paper provides a characterization of the size of the pores in the PMs of grapevine (Vitis vinifera). The PM porosity (PMP) of stems infected with the bacterium Xylella fastidiosa was compared with the PMP of healthy stems. Stems were infused with pressurized water and flow rates were determined; gold particles of known size were introduced with the water to assist in determining the size of PM pores. The effect of introducing trans-1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid (CDTA), oligogalacturonides, and polygalacturonic acid into stems on water flux via the xylem was also measured. The possibility that cell wall-degrading enzymes could alter the pore sizes, thus facilitating the ability of X. fastidiosa to cross the PMs, was tested. Two cell wall-degrading enzymes likely to be produced by X. fastidiosa (polygalactuoronase and endo-1,4-beta-glucanase) were infused into stems, and particle passage tests were performed to check for changes in PMP. Scanning electron microscopy of control and enzyme-infused stem segments revealed that the combination of enzymes opened holes in PMs, probably explaining enzyme impacts on PMP and how a small X. fastidiosa population, introduced into grapevines by insect vectors, can multiply and spread throughout the vine and cause Pierce's disease.
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    Perfect conductor and mu-metal enhancement of effects in electromagnetic fields over single emitters near topological insulators
    (2024) Dvorquez, Eitan; Pavez, Benjamin; Sun, Qiang; Pinto, Felipe; Greentree, Andrew D.; Gibson, Brant C.; Maze, Jeronimo R.
    We focus on the transmission and reflection coefficients of light in systems involving topological insulators (TIs). Due to the electromagnetic coupling in TIs, new mixing coefficients emerge, leading to new components of the electromagnetic fields of propagating waves. We have discovered a simple heterostructure that provides a 100-fold enhancement of the mixing coefficients for TI materials. Such effect depends on the TI's wave impedance and the selected material for the sublayer. We also predict a transverse deviation of the Poynting vector due to these mixed coefficients contributing to the radiative electromagnetic field of an electric dipole. Given an optimal configuration of the dipole-TI system, this deviation could amount to 0.28% of the Poynting vector due to emission near nontopological materials, making this effect detectable.