Effect of channel geometry on solute dispersion in pressure-driven microfluidic systems

Pressure-driven transport of fluid and solute samples is often desirable in microfluidic devices, particularly where sufficient electroosmotic flow rates cannot be realized or the use of an electric field is restricted. Unfortunately, this mode of actuation also leads to hydrodynamic dispersion due to the inherent fluid shear in the system. While such dispersivity is known to scale with the square of the Peclet number based on the narrower dimension of the conduit (often the channel depth), the proportionality constant can vary significantly depending on its actual cross section. In this article, we review previous studies to understand the effect of commonly microfabricated channel cross sections on the Taylor–Aris dispersion of solute slugs in simple pressure-driven flow systems. We also analyze some recently proposed optimum designs which can reduce the contribution to this band broadening arising from the presence of the channel sidewalls. Finally, new simulation results have been presented in the last section of this paper which describe solutal spreading due to bowing of microchannels that can occur from stresses developed during their fabrication or operation under high-pressure conditions.     

Utilization of ultrasound sensors for anti-collision systems of powered wheelchairs

Anti-collision systems have been developed for use with powered wheelchairs in order to enable people with cognitive or physical impairments to safely operate a powered wheelchair. Anti-collision systems consist of sensors that have the ability to detect objects near the wheelchair and a computer that can stop the chair if a collision is determined to be likely. This investigation considered the suitability of using ultrasound sensors in such a system when encountering objects typically found within a home or a long-term care facility. An ultrasound sensor's ability to detect an object was dependent on the object's size, shape, specularity, reflectivity, and sound absorption characteristics. Ultrasound sensors, by themselves, were found to be unsuitable for anti-collision systems due to an inability to detect objects commonly encountered in the target environment (the home or long-term care facility) without increasing the complexity of the system to such a degree that it would be prohibitive to deploy this technology to the public.     

The inherent price of indulgence

An indulgent algorithm is a distributed algorithm that tolerates asynchronous periods of the network when process crash detection is unreliable. This paper presents a tight bound on the time complexity of indulgent consensus algorithms. We consider a round-based eventually synchronous model, and we show that any t-resilient consensus algorithm in this model, requires at least t+2 rounds for a global decision even in runs that are synchronous. We contrast our lower bound with the well-known t+1 round tight bound on consensus in the synchronous model. We then prove the bound to be tight by exhibiting a new t-resilient consensus algorithm in the eventually synchronous model that reaches a global decision at round t+2 in every synchronous run. Our new algorithm is in this sense significantly faster than the most efficient indulgent algorithm we know of, which requires 2t+2 rounds in synchronous runs. Our lower bound applies to round-based consensus algorithms with unreliable failure detectors such as ⋄ P and ⋄ S, and our matching algorithm can be adapted to such failure detectors. This work is partially supported by the Swiss National Science Foundation (project number 510-207).     

Temperature dependence of threshold and electrical characteristics of InGaAsP-InP d.h. lasers

Measurements are reported of the electrical characteristics and temperature dependence of threshold current of InGaAsP-InP d.h. lasers (? = 1.3 ?m). Analysis of the I dV/dI characteristics of these devices indicates that drift leakage of carriers from the active region is not responsible for the high temperature sensitivity of threshold in this material system.     

Synthesis of DNA-polypyrrole nanocapsule

A template synthesis technique of encapsulating DNA molecules inside polypyrrole (PPy) nanotubes, termed as DNA-PPy nanocapsule, has been described here. The insertion of DNA molecules inside polypyrrole nanotubes is spontaneous in nature. The structural characterizations and possible applications of DNA-PPy nanocapsule in bio-sensing devices have been discussed.     

Equal-valued, common-terminal capacitor synthesis of RC one-ports

A method is presented for the synthesis of RC 1-ports with a minimum possible number of capacitors, all of equal value and all connected to a common terminal of the 1-port. Such a realisation facilitates economical integrated- circuit fabrication and is of importance in integrated active RC 2-port synthesis.     

Mathematical modeling of the blow-molding process

A mathematical simulation of the blow-molding cycle has been developed by combining general conservation principles along with appropriate constitutive relations for the material. A model of the parison formation stage has been devised by considering the competing effects due to swell and drawdown. A more rigorous numerical analysis of parison formation is also discussed. A theoretical treatment of parison inflation is described for both inelastic and viscoelastic materials by assuming uniform radial growth, Comparisons are made with experimental data for all phases of the molding cycle. The mathematical model is in reasonable quantitative agreement with experimental results and is capable of elucidating the influence of material properties and process conditions on the dynamics and performance of the blow-molding process.