Multiple conducting polymer microwire sensors

In this work, conducting polymer microwires of three commonly used conducting polymers were fabricated simultaneously on a common substrate using an intermediate-layer lithography (ILL) method. The three conducting polymers under consideration were polypyrrole (PPy), sulphonated polyaniline (SPANI) and poly(3,4-ethylenedioxythiophen)-poly(4-styrenesulphonate) (PEDOT-PSS). The fabricated microwires were implemented as sensing elements in detecting humidity and two organic vapors (i.e., methanol and acetone). The sensitivity of a single PPy microwire was compared with a rectangular PPy film after both were exposed to 45–85% humidity. The microwire sensor, due to its higher surface-to-volume ratio, was found to be more sensitive than the film sensor at low levels of humidity (between 45 and 58%). Beyond 58% humidity, the responses of the film and microwire sensors were similar. Three different sets of conducting polymer microwires (of PPy, SPANI and PEDOT) were then fabricated and employed as sensors to detect methanol, acetone and their mixtures. These microwires exhibited wave-like responses when they were exposed to these targets. The PPy and PEDOT microwires showed higher sensitivities in detecting methanol and acetone, respectively. The SPANI microwires exhibited similar responses in detecting methanol and acetone. The results demonstrate that microwire sensors were more effective than film sensors in detecting little quantities of target molecules. A sensor platform which integrates multiple microwire detectors is promising to detect multiple targets, and it also provides more information in detecting and distinguishing targets.     

Rapid macromolecular synthesis in a microfluidic channel with an oscillating flap

This study explores a method of enhancing the rates of macromolecular transport through a microchannel by introducing an oscillating mechanical flap in the fluidic system. A theoretical model is developed to determine the enhancement of macromolecular transport to a reaction site located along the channel surface. A numerical analysis is performed by considering a hinged flap located on the top or bottom walls of the channel. An order of magnitude analysis is conducted to estimate the reaction time which is bounded by the diffusion and the flow residence time. The period of oscillation is chosen to match the surface reaction time. The values of the characteristic flow variables adopted in this study, are representative of typical biomolecular transport processes confined to microscale geometries. With background flow, the results of the numerical analysis show that the mechanical actuator behaves like a miniature pump that drives a favorable gradient of macromolecules towards the surface reaction sites within an initial lapse of time. In a stagnant fluid, the results show that the moving flap behaves like a stirring agent bringing fluid with a higher concentration in contact with the reaction site and enhancing the surface concentration. In the latter case, the effect of the moving flap increases as the reaction progresses. The moving flap has the largest beneficial effect on surface concentration in the presence of a background flow when the position of the moving flap is along the top wall above the reaction site.     

Performance Evaluation of Controlled-Capacitor-Charging-Type Inverters

This paper presents the performance of capacitor-charging-type inverters. Both single- and three-phase inverters are considered. A simple technique to design the L -C elements of such an inverter is introduced. The switching devices are operated in the discontinuous conduction mode to reduce the size of the inductor and also for better dynamic performance. The inverter is simulated in PSPICE. An experimental prototype is produced to verify the results from simulation. Experimentations have been conducted for single-phase and three-phase systems. The inverter is found to operate satisfactorily for various types of load including unbalanced load.     

A Combined Circuit-Electromagnetic-Fluidic Computational Methodology for Force Prediction in Lab-on-Chip Environments

This paper focuses on a computational method for the simulation of the motion and manipulation of bio-particles using dielectrophoretic and micro-fluidic forces. The presented method uses surface integral equations for modeling both electromagnetic (EM) and fluidic domains. A coupled circuit-EM methodology is used to model electrical excitations. A steady Stokes flow is assumed for computing the fluidic traction forces. The resulting simulator accurately predicts the fields and forces on arbitrarily-shaped three dimensional particles representing bio-species. The presented methodology is amenable to acceleration with state of the art oct-tree-based fast matrix-vector schemes for rapid linear time iterative solution. This integrated computational approach leads to a pathway for rapid simulation of coupled circuit-EM-fluidic systems for Lab-on-chip (LoC) manipulation of biological species, which provides medical device designers the capability to augment control of bio-species, and explore new system designs     

High-performance E-mode AlGaN/GaN HEMTs

Enhancement-mode AlGaN/GaN high electron-mobility transistors have been fabricated with a gate length of 160 nm. The use of gate recess combined with a fluorine-based surface treatment under the gate produced devices with a threshold voltage of +0.1 V. The combination of very high transconductance (> 400 mS/mm) and low gate leakage allows unprecedented output current levels in excess of 1.2 A/mm. The small signal performance of these enhancement-mode devices shows a record current cutoff frequency (f/sub T/) of 85 GHz and a power gain cutoff frequency (f/sub max/) of 150 GHz.     

Study of Impact of Access Resistance on High-Frequency Performance of AlGaN/GaN HEMTs by Measurements at Low Temperatures

This letter studies the effect of access resistance on the high-frequency performance of AlGaN/GaN high-electron-mobility transistors. To systematically reduce the sheet access resistance, the transistors were measured at different temperatures. The increase of mobility at lower temperatures allowed more than four-fold reduction in the sheet access resistances. Both the current- and power-gain cutoff frequencies are observed to increase at low temperatures. Also, the intrinsic effective velocity has been estimated in these devices, as well as the parasitic delays involved in the final performance. Channel charging delay, which was expected to be most sensitive to parasitics, is observed to decrease at low temperatures. However, the drain delay, intrinsic delay, and effective electron velocity remain unaffected by temperature     

Static and dynamic modeling of solid oxide fuel cell using genetic programming

Modeling of solid oxide fuel cell (SOFC) systems is a powerful approach that can provide useful insights into the nonlinear dynamics of the system without the need for formulating complicated systems of equations describing the electrochemical and thermal properties. Several algorithmic approaches have in the past been reported for the modeling of solid oxide fuel cell stacks. However, all of these models have their limitations. This paper presents an efficient genetic programming approach to SOFC modeling and simulation. This method, belonging to the computational intelligence paradigm, is shown to outperform the state-of-the-art radial basis function neural network approach for SOFC modeling. Both static (fixed load) and dynamic (load transient) analyses are provided. Statistical tests of significance are used to validate the improvement in solution quality.     

On the effectiveness of movement prediction to reduce energy consumption in wireless communication

Node movement can be exploited to reduce the energy consumption of wireless network communication. The strategy consists in delaying communication until a mobile node moves close to its target peer node within an application- imposed deadline. We evaluate the performance of various heuristics that, based on the movement history of the mobile node, estimate an optimal time (in the sense of least energy use) of communication subject to the delay constraint. We evaluate the impact of the node movement model, length of movement history maintained, allowable delay, single hop versus multiple hop communication, and size of data transfer on the energy consumption. We also present measurement results on an iPAQ pocket PC that quantity energy consumption in executing the prediction algorithms. Our results show that, with relatively simple and, hence, efficient prediction heuristics, energy savings in communication can significantly outweigh the energy expenses in executing the prediction algorithms. Moreover, it is possible to achieve robust system performance across diverse node movement models.     

Mobility management for VoIP in 3G systems: evaluation of low-latency handoff schemes

The introduction of IP-based real-time services in next-generation mobile systems requires coupling mobility with quality of service. The mobility of the node can disrupt or even intermittently disconnect an ongoing real-time session. The duration of such an interruption is called disruption time or handover latency, and can heavily affect user satisfaction. Therefore, this delay needs to be minimized to provide good quality of VoIP services. In this article, we focus on network-layer mobility and mobile IP since it is a natural candidate for providing such mobility. We evaluate different low-latency schemes based on mobile IP and compare their performances in terms of disruption time for VoIP services. Low-latency handoffs are performed by anticipating and/or postponing the mobile IP registration process. With these methods, disruption time is reduced to 200 ms in most considered cases.     

Potassium intercalation of carbon onions ‘opened’ by carbon dioxide treatment

The potassium intercalation of onion-like carbon (OLC) samples consisting of aggregates of carbon onions is studied with photoemission spectroscopy. OLC samples were initially prepared by annealing nanodiamonds (3-20 nm in diameter) at 1800 K in vacuum. The resulting OLC consists of closed fullerene-like shells. The ‘closed’ OLC was subsequently treated with carbon dioxide at 1020 K in order to open the carbon shells by partial oxidation to create ‘opened’ OLC. Core level and valence band photoelectron spectroscopy have been employed in characterizing the changes in electronic structure of the samples. Upon intercalation of the closed OLC with K the C1s core level and valence band features shift to higher binding energies and the density of states at the Fermi level increases, while this effect is significantly smaller for intercalated opened OLC. These results indicate that opening the shells of carbon onions allows potassium to penetrate inside the particles and thus opens up a possible route to fill carbon onions with desired substances and their application as nanocapsules.