Mechanisms in damping of mechanical vibration by piezoelectric ceramic-polymer composite materials

The piezoelectric ceramic (piezoceramic) component of a polymer-piezoelectric ceramic composite converts mechanical energy into electrical energy and this electrical energy is dissipated as heat in a load resistance, R _x, simulated by a shunted resistance, but provided in practice by a conductive polymer composite matrix. The composite therefore dissipates the input mechanical energy via the damping mechanism provided by piezoelectric ceramic-conductive matrix material, as well as the conventional viscoelastic damping provided by the polymer. Mathematical models have been developed to characterize the damping behaviour of the composites, and the maximum damping ratio of composites can be as high as 23%. A two degrees-of-freedom (2DOF) experimental setup was developed to test the validity of the models. The experimental results are in good agreement with the theoretical predictions.     

The static and dynamic characteristics of single and multiplephase-shifted DFB laser structures

The influence of longitudinal mode spatial hole burning (LMSHB) on the performance of distributed feedback (DFB) laser structures is examined in detail. A comprehensive model has been used to interpret the experimental results and to construct a theoretical framework that was utilized to develop more advanced device designs. An increasing side mode intensity with output power, movement of the lasing mode relative to the stopband, and curvature of the light-current characteristic at low power can all be manifestations of the influence of LMSHB on the static device performance. The dynamic behavior can also be affected, with extended wavelength chirp and amplitude patterning effects on the timescale of the effective carrier recombination time being particularly important     

Primer-induced labeling of pea and field bean chromosomes in situ and in suspension

A protocol for primed in situ DNA labeling (PRINS) was optimized for pea (Pisum sativum L.) and field bean (Vicia faba L.) chromosomes attached to coverslips. Cloned DNA or synthetic oligonucleotides were used as probes for repetitive DNA sequences (rDNA, Fok-element) and different reaction conditions were tested to achieve the highest specific signal-to-background ratio. A procedure based on direct labeling by fluorescein-dUTP was compared with an indirect one using digoxigenin detected by fluorescently labeled antibody. Under optimal conditions, strong and specific signals were obtained exclusively on chromosome regions known to contain respective DNA sequences. Compared to the direct labeling, significantly stronger signals were obtained when the indirect procedure was used. Both types of labeling were successfully applied to chromosomes in suspension and were shown to produce signals comparable to that obtained with chromosomes attached to coverslips. It is expected that primed in situ DNA labeling en suspension (PRINSES) will provide a basis for flow-cytometric discrimination and sorting of otherwise indistinguishable chromosomes according to their specific fluorescent labeling.     

POP-IN AND CRACK ARREST IN AN HY80 WELD

It is generally thought that, when a material is in its brittle to ductile transition, it is more difficult to design for crack arrest than to prevent crack initiation (cleavage). This report shows that this is not always true for weldments. Comparison is made between compact crack arrest (CCA), K_a, and crack tip opening displacement (CTOD), K_Jc, toughness for the same HY80 weld. The value of K_a is shown to be much higher than the minimum K_Jc for pop-in fracture initiation. It is considered that the results support the conclusion of Japanese research workers (Arimochi and Isaka) that small pop-ins (in the CTOD test) propagate and arrest without load drop. It follows that prediction of structural failure for weldments need not be based on minimum pop-in toughness from CTOD tests.     

89-GHz fT room-temperature silicon MOSFETs

The authors report the implementation of deep-submicrometer Si MOSFETs that at room temperature have a unity-current-gain cutoff frequency (f_T) of 89 GHz, for a drain-to-source bias of 1.5 V, a gate-to-source bias of 1 V, a gate oxide thickness of 40 Å, and a channel length of 0.15 μm. The fabrication procedure is mostly conventional, except for the e-beam defined gates. The speed performance is achieved through an intrinsic transit time of only 1.8 ps across the active device region     

Fault tolerance in FFT arrays: Time redundancy approaches

Fault tolerance in VLSI/WSI FFT arrays acquires relevance when defects and run-time faults become significant, due to large dimensions of processors and arrays. Then, both restructuring to overcome end-of-production defects and reconfiguration to overcome run-time faults are required, to achieve the dual purposes of higher yield and higher reliability.Adopting as basic FFT network the two-dimensions array that directly corresponds to the FFT flow graph, the usual structure redundancy techniques tailored for two-dimensions arrays reconfiguration are not well applicable, since the limited locality of this network leads to relevant area increase due to the augmented interconnection structure.In this paper,time redundancy is suggested as a viable alternative for the two-dimensions FFT array; two different solutions are presented, one based oninter-stage reconfiguration, the other one adoptingintra-state reconfiguration, both allowing for survival to multiple faults with limited increase of network complexity and very small hard-core sections. As usual in many time redundancy methods, both approaches result in a processing speed equal to half the processing speed granted by an ideal, fault-free device.Reliability and survival ratios to multiple faults are evaluated for the two cases, taking into account also the area increments necessary for fault tolerance. The reliability evaluations allow for a direct comparison of the two solutions.     

Occlusion-resistant camera design for acquiring active environments.

In this article, we present a detailed theoretical analysis and a prototype implementation of a family of cameras designed with the explicit goal of detecting and removing interfering dynamic occluders in real time, during live capture, as opposed to fixing the resulting artifacts a posteriori. Such an early-acquisition approach improves efficiency: more valid samples are acquired faster without worrying about moving occluders. One option for designing a camera to be unaffected by moving occluders is to sample through the occluder, but true x-ray-like vision is technically impractical. Another option is to sample around the occluder using a camera with a large effective aperture, but such an approach requires a bulky acquisition device. Yet another possibility of sampling around an occluder is to rely on second and higher order reflected rays that indirectly sample surfaces not directly visible. However, devising an acquisition device sufficiently sensitive and efficient to capture large environments using reflected rays will remain challenging for the foreseeable future.     

Single-Step Granulation Method with Microwaves: Preliminary Studies and Pilot Scale Results

Common pharmaceutical excipients and compounds were dried either by a simple convection method or by a combined convection and microwave method in a static bed or by a combined microwave and vacuum method in a mixed bed. A simple placebo granulation was dried by an exclusive vacuum method and by a combined microwave and vacuum method in a mixed bed. The results were compared.