Excitation and detection of vibrations of micromechanical structures using a dielectric thin film

A new technique is introduced for both the excitation and the detection of vibrations of micromechanical structures. This makes use of a dielectric thin film, sandwiched between lower and upper electrodes, on top of the vibrating structure. The excitation is based on electrostatic forces between the charged electrodes, causing deformation of the dielectric film and bending of the multilayer structure. The detection of the vibration is capacitive, based on the fluctuation of the capacitance due to the deformation of the dielectric film. Experimental results for a stoichiometric silicon nitride dielectric film on top of a silicon cantilever agree well with predicted values. The yield of the electrostatic excitation as well as of the capacitive detection are satisfactory

Partitioning, extractability and formation of non-extractable PAH residues in soil: II. Effects on compound dissolution behaviour.

This study was carried out to assess the influence of PAH sequestration in sterile sewage sludge-amended arable soil on their dissolution behavior. Radiolabeled phenanthrene (14C-9-Phe), pyrene (14C-4,5,9,10-Pyr), and benzo[a]pyrene (14C-7-B[a]P) were spiked and aged for up to 525 days in sterile soil microcosms. The dissolution behavior of the compounds was determined at various times using an in-situ XAD-2 sorbent method. The XAD procedure allowed the detection of hydrophobic PAHs released from the soil and demonstrated that a fraction of PAH was resistant to dissolution. The experimental data generated was analyzed using an empirical two-site model, and fitted values were obtained for the magnitude of the rapidly released compound fraction and the rate of release for the rapid and slowly released compound fractions. Increasing sequestration did not reduce the size of the rapidly released compound fraction in this soil. We did, however, observe a decrease in the rate of the fast released fraction of 14C-7-B[a]P which formed a significantly larger sequestered fraction. The duration of the dissolution experiments proved insufficient to obtain precise estimations for the rate of slow compound release from the soil, and we were unable to determine whether sequestration affected the rate of release for the slowly released compound fraction. These results demonstrate the necessity of conducting desorption experiments for a period of months if complete data on the long-term release of desorption resistant compound fractions is to be obtained