Modeling and Prediction of the Dynamic Behaviour of Microbeams Under Electrostatic Load

This paper investigates the features of different techniques to model the dynamic behaviour of microbeams electrostatically actuated, mainly to identify the frequency shifting due to the electromechanical coupling. The aim is to define an engineering approach to be followed for a preliminary characterization of the microsystem. In a first part of the paper the main aspect addressed is the application of a systematic approach to write the equations of motion, applicable not only to this particular device, but in general to MEMs. The Lagrangian generalized method is outlined and applied to the current case of electromechanical coupling.A second issue concerns the application either of lumped or distributed parameters models, eventually discretized by FEM or equivalent techniques. A first model with a single degree of freedom of a double clamped microbeam is investigated: the analytic solution of the linearized equation of motion is compared to the numerical one of the nonlinear problem, solved by the Newmark's method. FEM models are then introduced and compared to the Newmark numerical integration applied to the single d.o.f. Although an accurate prediction of the nonlinear dynamic behaviour of the system can be drawn by the FEM-Newmark approach, a new procedure for a fast and preliminary estimation of the frequency response has been developed: the relationship between frequency and voltage is approximated by means of a parabolic curve based on two interpolation points, corresponding to the steady-state frequency (pure mechanical actuation) and to an arbitrary value of voltage, for which the Newmark's method is applied only once.     

Retention on non-polar adsorbents in liquid—solid chromatography Effect of grafted alkyl chains

The retention of 39 molecular probes was measured on chemically bonded dense layers of (3,3-dimethylbutyl)dimethylsiloxy (DMB) and tetradecyldimethylsiloxy (C₁₄) substituents on silica as a function of the composition of the binary acetonitrile-water eluent. The sign of the “associated system peak” was also noted. The composition dependence of retention, measured as areal retention volume, could be described on both non-polar stationary phases by the two-parameter Snyder-Soczewinski equation and by the three parameter Schoenmakers equation in a broad but restricted composition range. The areal retention volume on the surface with grafted alkyl chains was equal to or higher than that on the non-swellable, smooth, non-polar DMB surface. Additional retention on the C₁₄ surface increased with increasing adsorption force (retention) on the DMB surface and it was a function of the composition of the eluent. A possible interpretation of the sign of the “associated system peak” generated by the injection of a pure solute is also given in terms of salvation of the solute in the mobile phase and in terms of the modification of the non-polar adsorbent by the adsorbed solute.     

Conformational analysis: XXI—1H NMR study of 4,5-dimethyl-, 2,4,5-trimethyl- and 2,2,4,5-tetramethyl-1,3-dithiolanes

The 60 MHz ¹H NMR spectra of seven differently substituted 4,5-dimethyl-1,3-dithiolanes have been recorded and analysed. Configurational assignments are made and conformational aspects are discussed in the light of the spectral parameters.     

On Stephany's theory of origin of 1/f bulk noise

Summary Stephany's treatment is not correct since he neglects the friction force proportional to the velocity, which we show to be universal,i.e. present in any mechanism of electric conduction. Moreover his predicted power spectral density is in some cases three orders of magnitude larger than the observed one. Finally, his noise cannot be the true 1/f noise because it should predict a low cut-off of ∼5·10⁻² Hz due to the transit time of the electron-linked lattice (ELL) carriers through a distance of 20 μm while no cut-off has been observed down to 10⁻³ Hz.     

Ruthenium-Catalyzed Enantioselective Hydrogenation of 1,3-O-Disubstituted 1,3-Dihydroxypropan-2-ones

Optically active 1,3-O-disubstituted glycerols were obtained by enantioselective homogeneous hydrogenation of the corresponding 1,3-O-disubstituted 1,3-dihydroxypropan-2-ones with different Ru^II-binap complexes. The highest enantioselectivities were obtained with dimeric chloro-ruthenium complexes on the substrates bearing bulky trityloxy groups.     

Diastereoselective alkylations of oxazolidinone vinylogous glycolates

A highly Z-selective isomerization (double bond migration) was observed when oxazolidinone vinylogous glycolate was exposed to a strong base to give N-acyl oxazolidinone, bearing an electron rich olefin. The corresponding enolate was exposed to alkyl halides to provide alkylated compounds on the γ-position with respect to OBn group, with high regioselectivity and moderate diastereoselectivity. However, the nature of the chiral oxazolidinone leads to a significant increase in the reaction diastereoselectivity. A stereospecific formation of cis-olefin was also observed in these alkylated compounds.     

Versatile 2,7-substituted pyrene synthons for the synthesis of pyrene-fused azaacenes

A new synthetic route to prepare a series of versatile 2,7-substituted pyrene synthons for the synthesis of pyrene-fused azaacenes is described. By using such synthons, a library of eight pyrene-fused azacenes with different electronic structures and in most cases with enhanced solubility has been synthesized and characterized.     

Mesoporous aluminum phosphite

High surface area pure mesoporous aluminum-phosphorus oxide-based derivatives have been synthesized through an S⁺I⁻ surfactant-assisted cooperative mechanism by means of a one-pot preparative procedure from aqueous solution and starting from aluminum atrane complexes and phosphoric and/or phosphorous acids. A soft chemical extraction procedure allows opening the pore system of the parent as-prepared materials by exchanging the surfactant without mesostructure collapse. The nature of the pore wall can be modulated from mesoporous aluminum phosphate (ALPO) up to total incorporation of phosphite entities (mesoporous aluminum phosphite), which results in a gradual evolution of the acidic properties of the final materials. While phosphate groups in ALPO act as network building blocks (bridging Al atoms), the phosphite entities become basically attached to the pore surface, what gives practically empty channels. The mesoporous nature of the final materials is confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and N₂ adsorption–desorption isotherms. The materials present regular unimodal pore systems whose order decreases as the phosphite content increases. NMR spectroscopic results confirm the incorporation of oxo-phosphorus entities to the framework of these materials and also provide us useful information concerning the mechanism through which they are formed.