Hybrid passive/active inertial actuators to attenuate the structural response of a submerged hull

This paper theoretically investigates the application of tuned vibration absorbers and hybrid passive/active inertial actuators to reduce the vibrational responses of plates and shells. The passive/active actuators are initially applied to a simple plate. A model of a submerged hull consisting of a ring stiffened finite cylinder with bulkheads and external fluid loading is then considered. The fluctuating forces from the propeller result in excitation of the low frequency global hull modes. Inertial actuators and tuned vibration absorbers are located at each end of the hull and in circumferential arrays to reduce the hull structural response at its axial resonances. The control performance of the hybrid passive/active inertial actuator, where the passive component is tuned to a structural resonance, is compared to the attenuation achieved by a fully passive tuned vibration absorber. This work shows the potential of using hybrid passive/active inertial actuators to attenuate the global structural responses of a submerged vessel.

Lyapunov theory for zeno stability

Zeno behavior is a dynamic phenomenon unique to hybrid systems in which an infinite number of discrete transitions occurs in a finite amount of time. This behavior commonly arises in mechanical systems undergoing impacts and optimal control problems, but its characterization for general hybrid systems is not completely understood. The goal of this paper is to develop a stability theory for Zeno hybrid systems that parallels classical Lyapunov theory; that is, we present Lyapunov-like sufficient conditions for Zeno behavior obtained by mapping solutions of complex hybrid systems to solutions of simpler Zeno hybrid systems defined on the first quadrant of the plane. These conditions are applied to Lagrangian hybrid systems, which model mechanical systems undergoing impacts, yielding simple sufficient conditions for Zeno behavior. Finally, the results are applied to robotic bipedal walking. © 2012 IEEE.

Half-bridge SIC inverter for hybrid electric vehicles: Design, development and testing at higher operating temperature

In recent years, Silicon Carbide (SiC) semiconductor devices have shown promise for high density power electronic applications, due to their electrical and thermal properties. In this paper, the performance of SiC JFETs for hybrid electric vehicle (HEV) applications is investigated at heatsink temperatures of 100 °C. The thermal runaway characteristics, maximum current density and packaging temperature limitations of the devices are considered and the efficiency implications discussed. To quantify the power density capabilities of power transistors, a novel 'expression of rating' (EoR) is proposed. A prototype single phase, half-bridge voltage source inverter using SiC JFETs is also tested and its performance at 25 °C and 100 °C investigated.

Hybrid ventilation by revolving doors

The transfers of air driven by a revolving door connecting two rooms of initially different temperatures are investigated. The results of small-scale laboratory modelling show that a critical revolution rate exists for which transfers are maximal for a given combination of door geometry, revolution rate and temperature contrast. This critical revolution rate divides two possible transfer regimes for revolving doors. Potential implications of our findings to revolving door operation, to heat losses across the doorway and to ventilation driven by the door are discussed.

Learning based automatic face annotation for arbitrary poses and expressions from frontal images only

Statistical approaches for building non-rigid deformable models, such as the Active Appearance Model (AAM), have enjoyed great popularity in recent years, but typically require tedious manual annotation of training images. In this paper, a learning based approach for the automatic annotation of visually deformable objects from a single annotated frontal image is presented and demonstrated on the example of automatically annotating face images that can be used for building AAMs for fitting and tracking. This approach employs the idea of initially learning the correspondences between landmarks in a frontal image and a set of training images with a face in arbitrary poses. Using this learner, virtual images of unseen faces at any arbitrary pose for which the learner was trained can be reconstructed by predicting the new landmark locations and warping the texture from the frontal image. View-based AAMs are then built from the virtual images and used for automatically annotating unseen images, including images of different facial expressions, at any random pose within the maximum range spanned by the virtually reconstructed images. The approach is experimentally validated by automatically annotating face images from three different databases. © 2009 IEEE.

Multiwall nanotubes, multilayers, and hybrid nanostructures: new frontiers for technology and Raman spectroscopy.

Technological progress is determined, to a great extent, by developments in material science. Breakthroughs can happen when a new type of material or new combinations of known materials with different dimensionality and functionality are created. Multilayered structures, being planar or concentric, are now emerging as major players at the forefront of research. Raman spectroscopy is a well-established characterization technique for carbon nanomaterials and is being developed for layered materials. In this issue of ACS Nano, Hirschmann et al. investigate triple-wall carbon nanotubes via resonant Raman spectroscopy, showing how a wealth of information can be derived about these complex structures. The next challenge is to tackle hybrid heterostructures, consisting of different planar or concentric materials, arranged "on demand" to achieve targeted properties.

The vibro-acoustic analysis of built-up systems using a hybrid method with parametric and non-parametric uncertainties

An existing hybrid finite element (FE)/statistical energy analysis (SEA) approach to the analysis of the mid- and high frequency vibrations of a complex built-up system is extended here to a wider class of uncertainty modeling. In the original approach, the constituent parts of the system are considered to be either deterministic, and modeled using FE, or highly random, and modeled using SEA. A non-parametric model of randomness is employed in the SEA components, based on diffuse wave theory and the Gaussian Orthogonal Ensemble (GOE), and this enables the mean and variance of second order quantities such as vibrational energy and response cross-spectra to be predicted. In the present work the assumption that the FE components are deterministic is relaxed by the introduction of a parametric model of uncertainty in these components. The parametric uncertainty may be modeled either probabilistically, or by using a non-probabilistic approach such as interval analysis, and it is shown how these descriptions can be combined with the non-parametric uncertainty in the SEA subsystems to yield an overall assessment of the performance of the system. The method is illustrated by application to an example built-up plate system which has random properties, and benchmark comparisons are made with full Monte Carlo simulations. © 2012 Elsevier Ltd. All rights reserved.

Numerical study of the shielding properties of macroscopic hybrid ferromagnetic/superconductor hollow cylinders

We study the magnetic shielding properties of hybrid ferromagnetic/ superconductor (F/S) structures consisting of two coaxial cylinders, with one of each material. We use an axisymmetric finite-element model in which the electrical properties of the superconducting tube are modeled by a nonlinear E-J power law with a magnetic-field-dependent critical current density whereas the magnetic properties of the ferromagnetic material take saturation into account. We study and compare the penetration of a uniform axial magnetic field in two cases: 1) a ferromagnetic tube placed inside a larger superconducting tube (Ferro-In configuration) and 2) a ferromagnetic tube placed outside the superconducting one (Ferro-Out configuration). In both cases, we assess how the ferromagnetic tube improves the shielding properties of the sole superconducting tube. The influence of the geometrical parameters of the ferromagnetic tube is also studied: It is shown that, upon an optimal choice of the geometrical parameters, the range of magnetic fields that are efficiently shielded by the high-temperature superconductor tube alone can be increased by a factor of up to 7 (2) in a Ferro-Out (Ferro-In) configuration. The optimal configuration uses a 1020 carbon steel with a thickness of 2 mm and a height that is half that of the superconducting cylinder (80 mm). © 2009 IEEE.

Photoconductive hybrid films via directional self-assembly of C 60 on aligned carbon nanotubes

Hybrid nanostructured materials can exhibit different properties than their constituent components, and can enable decoupled engineering of energy conversion and transport functions. Novel means of building hybrid assemblies of crystalline C 60 and carbon nanotubes (CNTs) are presented, wherein aligned CNT films direct the crystallization and orientation of C 60 rods from solution. In these hybrid films, the C 60 rods are oriented parallel to the direction of the CNTs throughout the thickness of the film. High-resolution imaging shows that the crystals incorporate CNTs during growth, yet grazing-incidence X-ray diffraction (GIXD) shows that the crystal structure of the C 60 rods is not perturbed by the CNTs. Growth kinetics of the C 60 rods are enhanced 8-fold on CNTs compared to bare Si, emphasizing the importance of the aligned, porous morphology of the CNT films as well as the selective surface interactions between C 60 and CNTs. Finally, it is shown how hybrid C 60-CNT films can be integrated electrically and employed as UV detectors with a high photoconductive gain and a responsivity of 10 5 A W -1 at low biases (± 0.5 V). The finding that CNTs can induce rapid, directional crystallization of molecules from solution may have broader implications to the science and applications of crystal growth, such as for inorganic nanocrystals, proteins, and synthetic polymers. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Development of a hybrid ferrofluid seal technology for miniature pneumatic and hydraulic actuators

Future microrobotic applications require actuators that can generate a high actuation force and stroke in a limited volume. Up to now, little research has been performed on the development of pneumatic and hydraulic microactuators, although they offer great prospects in achieving high force densities. One of the main technological barriers in the development of these actuators is the fabrication of powerful seals with low leakage. This paper presents a seal technology for linear fluidic microactuators based on ferrofluids. A design and simulation method for these seals has been developed and validated by measurements on miniaturized actuator prototypes. These actuators have an outside diameter of 2 mm, a length of 13 mm and have been tested using both pressurized air and water. Our current actuator prototypes are able to operate at pressures up to 1.6 MPa without leakage. At these pressures, forces up to 0.65 N have been achieved. The stroke of the actuators is 10 mm. © 2009 Elsevier B.V. All rights reserved.

A hybrid surface tension seal for pneumatic and hydraulic microactuators

Recent research revealed that microactuators driven by pressurized fluids are able to generate high power and force densities at microscale. One of the main technological barriers in the development of these actuators is the fabrication low friction seals. This paper presents a novel scalable seal technology, which resists the actuation pressure relying on a combination of a clearance seal and a surface tension seal. This approach allows to seal pressures of more than 800 kPa without leakage. The seal is tested on an actuator with a bore of 0.8 mm2 and a length of 13 mm, which was able to generate forces up to 0.32 N. © 2008 Springer-Verlag.