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Vitis vinifera (Vitales: Vitaceae) as a Reproductive Host of Spissistilus festinus (Hemiptera: Membracidae).
Feeding by the three-cornered alfalfa hopper, Spissistilus festinus (Say) (Hemiptera: Membracidae) results in girdling of grapevine petioles and shoots. Its significance as an economic pest of grape has increased since it was shown to transmit Grapevine red blotch virus (GRBV) in a greenhouse study. However, the status of grapevines as a reproductive host for S. festinus remained undetermined. Adult S. festinus were caged onto three regions of the grapevines: apical shoot, green shoot, and dormant cane. Their ability to reproduce was determined by weekly destructive sampling for 7 wk. Successful oviposition and nymphal emergence were observed on apical and green shoots, but not on dormant canes. However, insect development beyond the second nymphal instar did not occur. Knowledge of S. festinus reproduction on grapevines will be an important consideration in designing management guidelines to minimize the spread of GRBV in vineyards
Dynamics of quartz tuning fork force sensors used in scanning probe microscopy
We have performed an experimental characterization of the dynamics of
oscillating quartz tuning forks which are being increasingly used in scanning
probe microscopy as force sensors. We show that tuning forks can be described
as a system of coupled oscillators. Nevertheless, this description requires the
knowledge of the elastic coupling constant between the prongs of the tuning
fork, which has not yet been measured. Therefore tuning forks have been usually
described within the single oscillator or the weakly coupled oscillators
approximation that neglects the coupling between the prongs. We propose three
different procedures to measure the elastic coupling constant: an
opto-mechanical method, a variation of the Cleveland method and a thermal noise
based method. We find that the coupling between the quartz tuning fork prongs
has a strong influence on the dynamics and the measured motion is in remarkable
agreement with a simple model of coupled harmonic oscillators. The precise
determination of the elastic coupling between the prongs of a tuning fork
allows to obtain a quantitative relation between the resonance frequency shift
and the force gradient acting at the free end of a tuning fork prong.Comment: 16 pages, 6 figures, 2 Table
Current rectification in a single molecule diode: the role of electrode coupling
We demonstrate large rectification ratios (> 100) in single-molecule
junctions based on a metal-oxide cluster (polyoxometalate), using a scanning
tunneling microscope (STM) both at ambient conditions and at low temperature.
These rectification ratios are the largest ever observed in a single-molecule
junction, and in addition these junctions sustain current densities larger than
10^5 A/cm^2. By following the variation of the I-V characteristics with
tip-molecule separation we demonstrate unambiguously that rectification is due
to asymmetric coupling to the electrodes of a molecule with an asymmetric level
structure. This mechanism can be implemented in other type of molecular
junctions using both organic and inorganic molecules and provides a simple
strategy for the rational design of molecular diodes
Force-gradient-induced mechanical dissipation of quartz tuning fork force sensors used in atomic force microscopy
We have studied the dynamics of quartz tuning fork resonators used in atomic
force microscopy taking into account mechanical energy dissipation through the
attachment of the tuning fork base. We find that the tuning fork resonator
quality factor changes even for the case of a purely elastic sensor-sample
interaction. This is due to the effective mechanical imbalance of the tuning
fork prongs induced by the sensor-sample force gradient which in turn has an
impact on the dissipation through the attachment of the resonator base. This
effect may yield a measured dissipation signal that can be different to the one
exclusively related to the dissipation between the sensor and the sample. We
also find that there is a second order term in addition to the linear
relationship between the sensor-sample force gradient and the resonance
frequency shift of the tuning fork that is significant even for force gradients
usually present in atomic force microscopy which are in the range of tens of
N/m.Comment: 9 pages, 3 figures and supplemental informatio
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