Microfabricated preconcentrator-focuser for a microscale gas chromatograph

The design, fabrication, and testing of a preconcentrator-focuser (PCF), consisting of a thick micromachined Si heater packed with a small quantity of a granular adsorbent material are described. The PCF is developed to capture and concentrate vapors for subsequent focused thermal desorption and analysis in a micro gas chromatograph. The microheater contains an array of high-aspect-ratio, etched-Si heating elements, 520 /spl mu/m (h)/spl times/50 /spl mu/m (w)/spl times/3000 /spl mu/m (l), bounded by an annulus of Si and thermally isolated from the remaining substrate by an air gap. This structure is sandwiched between Pyrex glass plates with inlet/outlet ports that accept capillary tubes for sample flow and is sealed by anodic bonding (bottom) and rapidly annealed glass/metal/Si solder bonding (top). The large microheater surface area allows for high adsorption capacity and efficient, uniform thermal desorption of vapors captured on the adsorbent within the structure. The adsorbent consists of roughly spherical granules, /spl sim/200 /spl mu/m in diameter, of a high-surface-area, graphitized carbon. Key design considerations, fabrication technologies, and results of performance tests are presented with an emphasis on the thermal desorption characteristics of several representative volatile organic compounds as a function of volumetric flow rates and heating rates. Preconcentration factors as high as 5600 and desorbed peak widths as narrow as 0.8 s are achieved from 0.25-L samples of benzene at modest heating rates. The effects of operating variables on sensitivity, chromatographic resolution, and detection limits are assessed. Testing of this PCF with a micromachined separation column and integrated sensor array is discussed briefly.     

Development of a nanofluidic preconcentrator with precise sample positioning and multi-channel preconcentration

A nanofluidic preconcentrator with the capability of rapidly preconcentrating and precisely positioning protein bands in multiple microchannels has been developed for highly sensitive detection of biomolecules. A novel electrical resistive network model is developed to guide the design of the nanofluidic preconcentrator which consists of a PDMS slab bonded with a glass slide. In the prototype design, two microchannels (23 mm long, 25–50 μm wide, and 5–15 μm deep), one preconcentration microchannel and one ground microchannel are connected in the middle via 16 nanochannels (25–50 μm long, 25 μm wide, and 50–80 nm deep). With two sets of optimal voltage settings applied on the opposite ends of the nanofluidic chip, the ion depletion region and electrokinetic trapping were generated to carry out the preconcentration. With the optimal voltage settings (30–30 V) predicted by the model, the ionic current of the nanochannel in our optimized preconcentrator was adjusted to be greater than the threshold value (3.9 nA) needed for the occurrence of the preconcentration, and a preconcentration factor >10⁵ was achieved in 5 min. The sample positioning capability of the preconcentrator was demonstrated by adjusting the applied voltages and moving the preconcentrated protein bands to multiple sites by a distance from several micrometers to several millimeters in the preconcentration channel. The multi-channel preconcentration capability was also demonstrated by preconcentrating two protein bands in two separate microchannels. In this work, the resistive network model was developed and validated to optimize nanofluidic preconcentrators for rapid, high throughput and highly sensitive sensing of low abundance analytes.     

Functionally testable path delay faults on a microprocessor

The impact of delay defects on these functionally untestable paths on overall circuit performance involves identification of such paths determining the achievable path delay fault coverage and reducing the subsequent test generation effort. The experimental results for two microprocessors (Parwan and DLX) indicate that a significant percentage of structurally testable paths are functionally untestable     

An energy-balanced swept-coverage mechanism for mobile WSNs

Coverage is one of the most important issues in Wireless Sensor Networks (WSNs). In literature, many coverage mechanisms have been proposed and employed mobile sensors to cover (heal) the coverage holes in the monitoring region. Consider that there are no redundant mobile sensors in a monitoring region. Some studies presented hole-movement mechanisms which used a mobile sensor to move a hole from one location to another, achieving the swept coverage of the monitoring region. However, in these studies, there are only some mobile sensors that participate in the hole-movement task, leading to an energy-unbalanced WSN. This paper considers a mobile WSN that contains holes and has no redundant mobile sensors to reach the spatial full coverage of the given monitoring region. To meet the swept coverage of the given monitoring region and balance the energies of mobile sensors, a distributed energy-balanced hole-movement mechanism, called EBHMM, is proposed. Theoretical analysis and performance evaluation reveal that the proposed EBHMM has better performance than existing hole-movement mechanisms in terms of the network lifetime and energy-balanced degree of mobile sensors.     

An optimal volute spiral case design for centrifugal fan: theoretical and experimental studies

An inverse design problem in determining the optimal shape of volute spiral case for a centrifugal-flow fan is examined in the present study using the Levenberg–Marquardt method and a general purpose commercial code CFD-ACE+, and based on a desired airflow rate. The desired volume airflow rate can be obtained by multiplying the airflow rate of an existing fan by a constant number which is >1. The shape of the redesigned volute case is generated using the equation of the trajectory of fluid particles in the volute, which enables the shape of the fan volute be constructed completely. Finally, prototypes of the original and optimized fan volutes as well as fan impellers are fabricated, thereafter the fan performance is tested based on the AMCA-210-85 standard to verify the validity of the design. The experimental results demonstrate that by utilizing the fabricated centrifugal optimal fan and operating at the design condition, the airflow rate can be increased by 6.5 % and the pressure drop, noise and input power of fan can be reduced by 1.6, 5.3 and 11.4 %, respectively, when compared with the original fan. As a result, the performance of optimal fan can be improved greatly.     

Tubular graphene architectures at the macroscopic scale: fabrication and properties

Specific graphene architectures at the macroscopic scale are paramount for exploring new functions and practical uses of graphene. In this study, macroscopic, freestanding, and tubular graphene (TG) architectures were successfully fabricated through a versatile and robust process based on the annealing of cellulose acetate (CA) on Ni templates. These TG architectures can be obtained as woven tubes with diameters of approximately 50 μm; they possess high graphitic crystallinity, strong electrical conductivity, and favorable corrosion resistance. The effects of processing parameters, such as annealing temperature, annealing time, and amount of CA, on the graphene properties of these architectures were investigated and are discussed in this paper. The graphene properties were characterized through field emission scanning electron microscopy, high-resolution transmission electron microscopy, atomic force microscopy, Raman spectroscopy, four-point probe resistivity, and electrochemical measurements.     

水基纳米聚硅乳液体系应用研究

制备了具有水分散性的疏水纳米聚硅,以水作为携带剂代替常规的有机分散剂,并将其用于低渗油田注水井的降压增注。通过分析宝浪油田储层孔喉特征,确定纳米聚硅的匹配粒径为10 20 nm。纳米聚硅乳液澄清透明,通过研究其分散性和稳定性,确定水基纳米增注液配方为1.75‰纳米聚硅、2‰助分散剂。水基纳米聚硅乳液可使岩石表面由亲水性变为强疏水性,接触角由23.7°增至131.8°。岩心流动实验结果表明,经水基纳米聚硅处理后,水相渗透率平均提高40%。对注污水或油转注的欠注井实施纳米聚硅増注前,进行酸化预处理可取得较好的增注效果。在宝浪油田5口井进行现场试验,增注有效率达80%,有效期可达一年以上。图6表4参14     

Reliability evaluation of class-E and class-a power amplifiers with nanoscaled CMOS technology

Circuit reliability of class-E and class-A power amplifiers is investigated based on a newly developed degradation subcircuit model. Measured degradation characteristics on the fabricated circuits agree well with the simulation predictions. Using this model, we have found that the class-E amplifier degrades faster than a class-A amplifier, due to a much higher stress level during switching. With a drastic decrease of PAE, a shorter lifetime is expected for a class-E amplifier.     

Influence of the presence of titanium oxide on the formation of pyrochlore phase in ferroelectric strontium bismuth tantalate ceramics

The effects of addition of TiO₂ on the formation of pyrochlore phase and dielectric properties of ferroelectric SrBi₂Ta₂O₉ have been investigated. When the content of Ti02 is less than 10 mol%, no secondary phases are produced, and SrBi₂Ta₂O₉-TiO₂ solid solutions are formed. However, with TiO₂ content ≥20 mol%, a pyrochlore phase is produced. Raising the content of TiO₂ in starting materials significantly increases the amounts of pyrochlore phase, and reduces the initial temperature for the formation of pyrochlore phase. The existence of TiO₂ also decreases the thermal stability of SrBi₂Ta₂O₉, causing the decomposition of SrBi₂Ta₂O₉to take place at lower temperatures. Furthermore, the presence of TiO₂ reduces the dielectric constants as well as remnant polarization of formed ceramics.     

Micellar layer-by-layer synthesis of TiO2/Ag hybrid particles for bactericidal and photocatalytic activities

Silver nanoparticles prepared by a reverse micelle process were sequentially deposited on rutile-structured TiO₂ particles via an electrostatic layer-by-layer (LbL) deposition together with a hydrophilic/hydrophobic interaction. The TiO₂ surface was first mediated by a preferential adsorption of poly(allylamine hydrochloride) (PAH) cationic molecules, before being mixed with the Ag nanoparticles encapsulated in reverse micelles consisting of anionic surfactant of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in isooctane. The deposition of Ag nanoparticles was not of a uniform coverage on the TiO₂ surface, but of a heterogeneous growth of the Ag particles on the TiO₂ surface. Antibacterial activity of the composites against gram-negative bacteria, i.e., Escherichia coli (E. coli), was found to increase with the deposition cycle, resulted mainly from the increased Ag concentration. The bactericidity is persistent in the absence of ultraviolet (UV) light. Over the concentration range of Ag examined, i.e., Ag/Ti atomic ratio varies from 0.28% to 0.53%, photocatalytic efficiency of the composites against methylene blue (MB) dye in an aqueous solution also improved pronouncedly with the silver concentration under UV exposure.