Simple and functional photonic devices from printable liquid crystal lasers

In this paper we demonstrate laser emission from emulsion-based polymer dispersed liquid crystals. Such lasers can be easily formed on single substrates with no alignment layers. Remarkably, it is shown that there can exist two radically different laser emission profiles, namely, photonic band-edge lasing and non-resonant random lasing. The emission is controlled by simple changes in the emulsification procedure. Low mixing speeds generate larger droplets that favor photonic band edge lasing with the requisite helical alignment produced by film shrinkage. Higher mixing speeds generate small droplets, which facilitate random lasing by a non-resonant scattering feedback process. Lasing thresholds and linewidth data are presented showing the potential of controllable linewidth lasing sources. Sequential and stacked layers demonstrate the possibility of achieving complex, simultaneous multi-wavelength and "white-light" laser output from a wide variety of substrates including glass, metallic, paper and flexible plastic. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).

SoC energy savings = reduce+reuse+recycle: A case study using a 660MHz DC-DC converter with integrated output filter

This paper advocates 'reduce, reuse, recycle' as a complete energy savings strategy. While reduction has been common to date, there is growing need to emphasize reuse and recycling as well. We design a DC-DC buck converter to demonstrate the 3 techniques: reduce with low-swing and zero voltage switching (ZVS), reuse with supply stacking, and recycle with regulated delivery of excess energy to the output load. The efficiency gained from these 3 techniques helps offset the loss of operating drivers at very high switching frequencies which are needed to move the output filter completely on-chip. A prototype was fabricated in 0.18μm CMOS, operates at 660MHz, and converts 2.2V to 0.75-1.0V at ∼50mA.1 © 2008 IEEE.

A 660MHz ZVS DC-DC converter using gate-driver charge-recycling in 0.18μm CMOS with an integrated output filter

The design and manufacture of a prototype chip level power supply is described, with both simulated and experimental results. Of particular interest is the inclusion of a fully integrated on-chip LC filter. A high switching frequency of 660MHz and the design of a device drive circuit reduce losses by supply stacking, low-swing signaling and charge recycling. The paper demonstrates that a chip level converter operating at high frequency can be built and shows how this can be achieved, using zero voltage switching techniques similar to those commonly used in larger converters. Both simulations and experimental data from a fabricated circuit in 0.18μm CMOS are included. The circuit converts 2.2V to 0.75∼1.0V at ∼55mA. ©2008 IEEE.

Initial modelling and controller design for active control of spacecraft microvibrations

Microvibrations, at frequencies between 1 and 1000 Hz, generated by on board equipment, propagate throughout a spacecraft structure affecting the performance of sensitive payloads. The purpose of this work is to investigate strategies to model and reduce these dynamic disturbances by active control. Initial studies were performed by considering a mass loaded panel where the disturbance excitation source consisted of point forces, the objective being to minimise the displacement at an arbitrary output location. Piezoelectric patches acting as sensors and actuators were used. The equations of motion are derived by using Lagrange's equation with modal shapes as Ritz functions. The number of sensors/actuators and their location is variable. The set of equations obtained is then transformed into state variables and some initial controller design studies have been undertaken. These are based on feedback control implemented using a full state feedback and an observer which reconstructs the state vector from the available sensor signal. Here, the basics behind the structural modelling and controller design will be described. This preliminary analysis will also be used to identify short to medium term further work.

Global state synchronization in networks of cyclic feedback systems

This technical note studies global asymptotic state synchronization in networks of identical systems. Conditions on the coupling strength required for the synchronization of nodes having a cyclic feedback structure are deduced using incremental dissipativity theory. The method takes advantage of the incremental passivity properties of the constituent subsystems of the network nodes to reformulate the synchronization problem as one of achieving incremental passivity by coupling. The method can be used in the framework of contraction theory to constructively build a contracting metric for the incremental system. The result is illustrated for a network of biochemical oscillators. © 2011 IEEE.

Visuomotor feedback gains upregulate during the learning of novel dynamics.

At an early stage of learning novel dynamics, changes in muscle activity are mainly due to corrective feedback responses. These feedback contributions to the overall motor command are gradually reduced as feedforward control is learned. The temporary increased use of feedback could arise simply from the large errors in early learning with either unaltered gains or even slightly downregulated gains, or from an upregulation of the feedback gains when feedforward prediction is insufficient. We therefore investigated whether the sensorimotor control system alters feedback gains during adaptation to a novel force field generated by a robotic manipulandum. To probe the feedback gains throughout learning, we measured the magnitude of involuntary rapid visuomotor responses to rapid shifts in the visual location of the hand during reaching movements. We found large increases in the magnitude of the rapid visuomotor response whenever the dynamics changed: both when the force field was first presented, and when it was removed. We confirmed that these changes in feedback gain are not simply a byproduct of the change in background load, by demonstrating that this rapid visuomotor response is not load sensitive. Our results suggest that when the sensorimotor control system experiences errors, it increases the gain of the visuomotor feedback pathways to deal with the unexpected disturbances until the feedforward controller learns the appropriate dynamics. We suggest that these feedback gains are upregulated with increased uncertainty in the knowledge of the dynamics to counteract any errors or disturbances and ensure accurate and skillful movements.

Plasma stabilisation of metallic nanoparticles on silicon for the growth of carbon nanotubes

Ammonia (NH 3) plasma pretreatment is used to form and temporarily reduce the mobility of Ni, Co, or Fe nanoparticles on boron-doped mono- and poly-crystalline silicon. X-ray photoemission spectroscopy proves that NH 3 plasma nitrides the Si supports during nanoparticle formation which prevents excessive nanoparticle sintering/diffusion into the bulk of Si during carbon nanotube growth by chemical vapour deposition. The nitridation of Si thus leads to nanotube vertical alignment and the growth of nanotube forests by root growth mechanism. © 2012 American Institute of Physics.

Evaluation of multi-sensory feedback on the usability of a virtual assembly environment

Virtual assembly environment (VAE) technology has the great potential for benefiting the manufacturing applications in industry. Usability is an important aspect of the VAE. This paper presents the usability evaluation of a developed multi-sensory VAE. The evaluation is conducted by using its three attributes: (a) efficiency of use; (b) user satisfaction; and (c) reliability. These are addressed by using task completion times (TCTs), questionnaires, and human performance error rates (HPERs), respectively. A peg-in-a-hole and a Sener electronic box assembly task have been used to perform the experiments, using sixteen participants. The outcomes showed that the introduction of 3D auditory and/or visual feedback could improve the usability. They also indicated that the integrated feedback (visual plus auditory) offered better usability than either feedback used in isolation. Most participants preferred the integrated feedback to either feedback (visual or auditory) or no feedback. The participants' comments demonstrated that nonrealistic or inappropriate feedback had negative effects on the usability, and easily made them feel frustrated. The possible reasons behind the outcomes are also analysed. © 2007 ACADEMY PUBLISHER.