Displacement amplification of piezoelectric microactuators with a micromachined leverage unit

One of the so-called Aero-MEMS applications is the drag reduction on airfoils by using an array of dedicated microactuators. When applying active wave cancellation principles in thin transitional boundary layers, these actuators need to exhibit relatively large stroke at relatively high operational frequencies. For this purpose, a novel micromachined mechanical amplification unit for increasing the stroke of piezoelectric microactuators up to high frequencies is presented in this paper. The mechanical lever is provided by a silicon membrane, sliced in a cake-like fashion. The fabrication and assembly process as well as results of dynamic simulations and experimental measurements are reported. For frequencies from quasi-static up to 15 kHz and for varying spacer positions, an amplification ratio of 5–13 is obtained when comparing displacements at the piezoelement and at the lever tip. Results from finite element simulations were found to be in good agreement with experiments. Finally, the application of these microactuators on airfoils for manipulating the transition point between laminar and turbulent flow conditions is discussed.     

Numerical simulation of steady compressible flows using a zonal formulation. Part I: inviscid flows

Simulation of inviscid flows are usually based on the Euler equations, namely, conservation laws of mass, momentum, and energy written in terms of conservative variables. We present an alternative formulation where the velocity components are calculated from a generalized form of the Cauchy–Riemann equations with a non-homogeneous term representing vorticity. The vorticity is obtained in terms of the gradients of entropy and total enthalpy via Crocco's relation (an expression of the normal momentum equation). The entropy and the total enthalpy are calculated from the tangential momentum and energy equations. For external aerodynamics, most of the field is isentropic and irrotational, and the formulation reduces to potential flow. Hence, two zones are easily identifiable. An inner zone where vorticity could be important, and an outer zone where vorticity is negligible. Preliminary results for two and three dimensional transonic flows over airfoils and wings are presented and compared with standard Euler calculations.     

Relationship between resazurin reduction test, reactive oxygen species generation, and gamma-glutamyltransferase

The production of reactive oxygen species (ROS) from spermatozoa has been measured by chemiluminescence in the two fractions of a Percoll gradient column (47 and 90%). Chemiluminescent signals were recorded in each fraction after addition of luminol and horse-radish peroxidase (basal state), and after stimulation with formyl-methionyl-leucyl-phenyl-alanine (FMLP) and phorbol ester (PMA). We found an inverse correlation between the reducing capacity of the semen as estimated by the resazurin test, and the production of ROS by the spermatozoa, especially after stimulation with PMA (r = 0.51, P < 0.001). gamma-glutamyltransferase activity of seminal plasma was inversely correlated with ROS (r = -0.47, P < 0.01) and the resazurin test result (r = -0.43, P < 0.001) suggesting a possible role of prostatic secretions in the protection of spermatozoa against oxygen radicals. The resazurin test has a positive predictive value of 92.5% at a criterion value of colour scale 4 to discriminate between normal and excessive ROS production by spermatozoa, with sensitivity 79% and specificity 74%. In addition, at criterion value of colour scale 3, the resazurin test could distinguish between samples with normal or low activity of gamma-glutamyltransferase, with sensitivity 57% and specificity 93%. It is concluded that the result of the resazurin test can be influenced by the oxidative stress of spermatozoa and by prostatic function.     

Molecular dynamics modeling of cavity strengthening in irradiated iron

One of the most important problems in the field of nuclear industry is the relationship between irradiation-induced damage and the resulting induced mechanical response of the target metal and in particular ferritic base steels. In this work molecular dynamics simulation is used to simulate the nanoscale interaction between a moving dislocation and a defect, such as a cavity, as void or He bubble. The stress–strain curves are obtained under imposed strain rate condition using the atomic potentials based on the Fe potential of Ackland et al. 1997 for a void and He bubble as a function of He content and temperature. It appears that a 2 nm void is a stronger obstacle than a He bubble at low He contents, whereas at high He contents, the He bubble becomes a stronger obstacle. With increasing temperature the escape stress decreases and at the same time there is increasing degeneracy in the type of interaction.     

Low-power high-speed operation of submicron InP-InGaAs SHBTs at 1 mA

Scaling of submicron InP-InGaAs HBTs is investigated for low-power high-speed applications in mixed signal circuits. Device performance for transistors fabricated with a 0.5-/spl mu/m emitter width and varying emitter lengths are studied. The 0.5 /spl mu/m/spl times/2 /spl mu/m devices yielded excellent low-current RF performance, with an f/sub T/=173 GHz and an f/sub MAX/=187 GHz at 1 mA, the highest values reported for InP-based devices to date.     

Improved numerical simulations of incompressible flows based on viscous/inviscid interaction procedures

Viscous/inviscid interaction procedures consist usually of coupling potential flow and boundary layer calculations. In this study, the interaction is modeled using Helmholtz-type velocity decomposition where the gradient of the potential is augmented with a correction accounting for the vorticity effects in the viscous layers. Different ways to calculate the rotational components are discussed and methods to systematically improve the model are studied. Numerical results are compared with standard Navier–Stokes calculations to justify the present approach.     

The dynamic effects in vibrating-plate and pulsed extractors—II. The forces under the steady and pulsating single-phase flow

The experimental results are presented of the friction losses under the steady flow of liquid through plates of various construction. Under the laminar and fully turbulent regime of the flow the experimental data agree well with the derived relations and an empirical relation is given for the transition regime. The measurements are carried out of the forces and pressures existing under plate vibrations and an analysis of the experimental data shows that the equivalent thickness of the plate, expressing the effect on inertia forces under pulsating flow, is a periodic function of time. An empirical correlation for this quantity is found and the set of equations for the calculation of the forces, pressures and the instantaneous and average power input thus completed. A simple empirical relation for the average power input is provided.     

A Novel IDFT/DFT Based Transceiver for Faster than Nyquist Signaling Optimization

Wireless Personal Communications - Future radio communication systems become user-centric and lay more emphasize on individual quality-of-service (QoS) experience than system-wide performance....